@martinhjelmare
Sorry, I was away from the computer for a little while.
I did reuse an old node id, that could have been the problem.
Assigned a new node ID and this is where I stand now:
Firts up: the node sketch:
/**
 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 *
 * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
 * Copyright (C) 2013-2015 Sensnology AB
 * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
 *
 * Documentation: http://www.mysensors.org
 * Support Forum: http://forum.mysensors.org
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 *******************************
 *
 * REVISION HISTORY
 * Version 1.0 - Henrik EKblad
 *
 * DESCRIPTION
 * This sketch provides an example how to implement a humidity/temperature
 * sensor using DHT11/DHT-22
 * http://www.mysensors.org/build/humidity
 */
#include <SPI.h>
#include <MySensor.h>
#include <DHT.h>
#define DIGITAL_INPUT_MOTION 3   // The digital input you attached your motion sensor.  (Only 2 and 3 generates interrupt!)
#define INTERRUPT DIGITAL_INPUT_MOTION-2 // Usually the interrupt = pin -2 (on uno/nano anyway)
#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1
#define CHILD_ID_MOT 2
#define HUMIDITY_SENSOR_DIGITAL_PIN 4
unsigned long SLEEP_TIME = 15000; // Sleep time between reads (in milliseconds)
MySensor gw;
DHT dht;
float lastTemp;
float lastHum;
boolean metric = true;
MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
MyMessage msgMot(CHILD_ID_MOT, V_TRIPPED);
int node_id = 20;
boolean lastTripped = false ;
void setup()
{
  gw.begin(NULL, node_id);
  dht.setup(HUMIDITY_SENSOR_DIGITAL_PIN);
  // Send the Sketch Version Information to the Gateway
  gw.sendSketchInfo("Humidity and motion", "1.0");
  pinMode(DIGITAL_INPUT_MOTION, INPUT);      // sets the motion sensor digital pin as input
  // Register all sensors to gw (they will be created as child devices)
  gw.present(CHILD_ID_HUM, S_HUM);
  gw.present(CHILD_ID_TEMP, S_TEMP);
  gw.present(CHILD_ID_MOT, S_MOTION);
  metric = gw.getConfig().isMetric;
}
void loop()
{
  /* int wake;
  wake = gw.sleep(INTERRUPT, CHANGE, SLEEP_TIME);
   if (wake == 1) {
     Serial.println("wake by motion");
     Serial.println("reading motion");
     motion();
   }
   else {
     Serial.println("wake by timer");
     Serial.println("reading motion");
     motion();
     Serial.println("reading temp/hum");
     humTemp();
   }
  */
  motion();
  
  Serial.println("read temp / hum");
  humTemp();
  Serial.println("going to sleep now.");
  gw.sleep(INTERRUPT, CHANGE, SLEEP_TIME); //sleep a bit
}
void motion() {
  // Read digital motion value
  boolean tripped = digitalRead(DIGITAL_INPUT_MOTION);
  Serial.println(tripped);
  if (lastTripped != tripped) {
    gw.send(msgMot.set(tripped ? "1" : "0")); // Send tripped value to gw
    lastTripped = tripped;
  }
}
void humTemp() {
  gw.wait(dht.getMinimumSamplingPeriod());
  float temperature = dht.getTemperature();
  if (isnan(temperature)) {
    Serial.println("Failed reading temperature from DHT");
  } else if (temperature != lastTemp) {
    lastTemp = temperature;
    if (!metric) {
      temperature = dht.toFahrenheit(temperature);
    }
    gw.send(msgTemp.set(temperature, 1));
    Serial.print("T: ");
    Serial.println(temperature);
  }
  float humidity = dht.getHumidity();
  if (isnan(humidity)) {
    Serial.println("Failed reading humidity from DHT");
  } else if (humidity != lastHum) {
    lastHum = humidity;
    gw.send(msgHum.set(humidity, 1));
    Serial.print("H: ");
    Serial.println(humidity);
  }
}
Now, my HA config:
homeassistant:
  # Name of the location where Home Assistant is running
  name: Home
  # Location required to calculate the time the sun rises and sets
  latitude: xxxxxxxx
  longitude: xxxxxxxxxxxxxx
  # C for Celcius, F for Fahrenheit
  temperature_unit: C
  # Pick yours from here: http://en.wikipedia.org/wiki/List_of_tz_database_time_zones
  time_zone: Europe/Brussels
# View all events in a logbook
logbook:
# Checks for available updates
updater:
# Discover some devices automatically
discovery:
# Track the sun
sun:
# Allows you to issue voice commands from the frontend
conversation:
# Enables support for tracking state changes over time.
history:
# Enables the frontend
frontend:
# Show links to resources in log and frontend
introduction:
mysensors:
  gateways:
    - port: '/dev/MSgw'
  debug: true
  persistence: false
and the output when starting hass:
Config directory: /home/pi/.homeassistant
WARNING:homeassistant.bootstrap:Colorlog package not found, console coloring disabled
INFO:homeassistant.core:Bus:Handling <Event service_registered[L]: domain=homeassistant, service=turn_off>
INFO:homeassistant.core:Bus:Handling <Event service_registered[L]: domain=homeassistant, service=turn_on>
INFO:homeassistant.bootstrap:Home Assistant core initialized
INFO:homeassistant.loader:Loaded logbook from homeassistant.components.logbook
INFO:homeassistant.loader:Loaded recorder from homeassistant.components.recorder
INFO:homeassistant.loader:Loaded http from homeassistant.components.http
INFO:homeassistant.loader:Loaded history from homeassistant.components.history
INFO:homeassistant.loader:Loaded introduction from homeassistant.components.introduction
INFO:homeassistant.loader:Loaded updater from homeassistant.components.updater
INFO:homeassistant.loader:Loaded conversation from homeassistant.components.conversation
INFO:homeassistant.loader:Loaded discovery from homeassistant.components.discovery
INFO:homeassistant.loader:Loaded mysensors from homeassistant.components.mysensors
INFO:homeassistant.loader:Loaded frontend from homeassistant.components.frontend
INFO:homeassistant.loader:Loaded api from homeassistant.components.api
INFO:homeassistant.loader:Loaded sun from homeassistant.components.sun
INFO:homeassistant.components.introduction:
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        Hello, and welcome to Home Assistant!
        We'll hope that we can make all your dreams come true.
        Here are some resources to get started:
         - Configuring Home Assistant:
           https://home-assistant.io/getting-started/configuration/
         - Available components:
           https://home-assistant.io/components/
         - Troubleshooting your configuration:
           https://home-assistant.io/getting-started/troubleshooting-configuration/
         - Getting help:
           https://home-assistant.io/help/
        This message is generated by the introduction component. You can
        disable it in configuration.yaml.
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=introduction>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=recorder>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=http>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=logbook>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=history>
INFO:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): pypi.python.org
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=updater>
/home/pi/.homeassistant/lib/fuzzywuzzy/fuzz.py:33: UserWarning: Using slow pure-python SequenceMatcher. Install python-Levenshtein to remove this warning
  warnings.warn('Using slow pure-python SequenceMatcher. Install python-Levenshtein to remove this warning')
INFO:homeassistant.core:Bus:Handling <Event service_registered[L]: domain=conversation, service=process>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=conversation>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=discovery>
INFO:homeassistant.loader:Loaded sensor from homeassistant.components.sensor
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=sensor>
INFO:homeassistant.core:Bus:Handling <Event platform_discovered[L]: discovered=, service=mysensors.sensors>
INFO:homeassistant.loader:Loaded sensor.mysensors from homeassistant.components.sensor.mysensors
INFO:homeassistant.loader:Loaded switch from homeassistant.components.switch
INFO:homeassistant.core:Bus:Handling <Event service_registered[L]: domain=switch, service=turn_off>
INFO:homeassistant.core:Bus:Handling <Event service_registered[L]: domain=switch, service=turn_on>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=switch>
INFO:homeassistant.core:Bus:Handling <Event platform_discovered[L]: discovered=, service=mysensors.switches>
INFO:homeassistant.loader:Loaded switch.mysensors from homeassistant.components.switch.mysensors
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=mysensors>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=api>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=frontend>
INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): maps.googleapis.com
INFO:homeassistant.core:Bus:Handling <Event state_changed[L]: new_state=<state sun.sun=below_horizon; next_setting=16:19:22 25-01-2016, friendly_name=Sun, next_rising=07:29:47 25-01-2016, elevation=-33.1 @ 20:51:46 24-01-2016>, entity_id=sun.sun>
INFO:homeassistant.core:Bus:Handling <Event component_loaded[L]: component=sun>
INFO:homeassistant.core:Starting Home Assistant (16 threads)
INFO:homeassistant.core:Bus:Handling <Event homeassistant_start[L]>
INFO:homeassistant.core:Bus:Handling <Event service_registered[L]: domain=homeassistant, service=stop>
INFO:homeassistant.components.http:Starting web interface at http://0.0.0.0:8123
INFO:homeassistant.core:Timer:starting
INFO:mysensors.mysensors:Trying to connect to /dev/MSgw
INFO:homeassistant.components.http:"GET /api/stream?api_password=no_password_set&restrict=state_changed,component_loaded,service_registered HTTP/1.1" 200 -
INFO:homeassistant.components.http:"GET /api/stream?api_password=no_password_set&restrict=state_changed,component_loaded,service_registered HTTP/1.1" 200 -
INFO:homeassistant.components.http:"GET /api/bootstrap HTTP/1.1" 200 -
INFO:netdisco.service:Scanning
INFO:homeassistant.components.http:"GET /api/bootstrap HTTP/1.1" 200 -
INFO:mysensors.mysensors:/dev/MSgw is open...
INFO:mysensors.mysensors:Connected to /dev/MSgw
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:gateway started, id=0, parent=0, distance=0
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:read: 20-20-0 s=0,c=1,t=1,pt=7,l=5,sg=0:54.0
INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): 192.168.1.70
INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): 192.168.1.70
INFO:requests.packages.urllib3.connectionpool:Starting new HTTP connection (1): 192.168.1.1
INFO:homeassistant.components.discovery:Found new service: DLNA http://192.168.1.70:1972/DeviceDescription.xml
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:read: 20-20-0 s=0,c=1,t=1,pt=7,l=5,sg=0:53.0
INFO:homeassistant.core:Bus:Handling <Event state_changed[L]: new_state=<state sun.sun=below_horizon; next_setting=16:19:22 25-01-2016, friendly_name=Sun, next_rising=07:29:47 25-01-2016, elevation=-33.21 @ 20:51:46 24-01-2016>, entity_id=sun.sun, old_state=<state sun.sun=below_horizon; next_setting=16:19:22 25-01-2016, friendly_name=Sun, next_rising=07:29:47 25-01-2016, elevation=-33.1 @ 20:51:46 24-01-2016>>
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:read: 20-20-0 s=0,c=1,t=1,pt=7,l=5,sg=0:54.0
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:read: 20-20-0 s=0,c=1,t=1,pt=7,l=5,sg=0:53.0
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:read: 20-20-0 s=0,c=1,t=1,pt=7,l=5,sg=0:54.0
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:read: 20-20-0 s=0,c=1,t=1,pt=7,l=5,sg=0:53.0
INFO:homeassistant.core:Bus:Handling <Event state_changed[L]: new_state=<state sun.sun=below_horizon; next_setting=16:19:22 25-01-2016, friendly_name=Sun, next_rising=07:29:47 25-01-2016, elevation=-33.36 @ 20:51:46 24-01-2016>, entity_id=sun.sun, old_state=<state sun.sun=below_horizon; next_setting=16:19:22 25-01-2016, friendly_name=Sun, next_rising=07:29:47 25-01-2016, elevation=-33.21 @ 20:51:46 24-01-2016>>
INFO:mysensors.mysensors:n:0 c:0 t:3 s:9 p:read: 20-20-0 s=0,c=1,t=1,pt=7,l=5,sg=0:54.0
INFO:homeassistant.components.http:"GET /states HTTP/1.1" 200 -
INFO:homeassistant.components.http:"GET /static/frontend-1003c31441ec44b3db84b49980f736a7.html HTTP/1.1" 200 -
INFO:homeassistant.components.http:"GET /static/favicon-192x192.png HTTP/1.1" 200 -
INFO:homeassistant.components.http:"GET /static/favicon.ico HTTP/1.1" 200 -
INFO:homeassistant.components.http:"GET /api/bootstrap HTTP/1.1" 200 -
INFO:homeassistant.components.http:"GET /api/stream?api_password=no_password_set&restrict=state_changed,component_loaded,service_registered HTTP/1.1" 200 -
I don't get errors anymore, but nothing shows up in the web interface.
I think the messages aren't being interpreted?