@update
OK - just following this up with extra info.
Previously, I was using radios without the cap.
Once a 47 uf cap was added, I didn't need the extra power supplies (the USB power was enough to the Uno clones).
Thinking about this now, It wasn't the uno boards, it must have been noise/weak power on my laptop USB.

Also, I wasted a lot of time on a bad rf24L01 board ( I think I bust it a while ago by supplying 5v ).
So, the moral of the story?

• If you get a message saying "radio bad" - try another rf24l01
• ALWAYS add a capacitor to every rf2401 board

SUCCESS! - My "ESP8266 MQTT gateway" sketch now works OK - no need for a 3rd device
*EDIT I've been using this board and the problem is ....

I'M USING THE BOARD PICTURED BELOW AND THE LABELS FOR GPIO4 and GPIO5 ARE THE WRONG WAY ROUND (screen print error)

I swapped the cable from the header pin marked GPIO4 to GPIO5 and everything worked fine. I'm wondering if this is the same solution for a lot of people here (I've put this info on build page)
https://github.com/esp8266/Arduino/issues/437
https://twitter.com/bdcatalin/status/663434209265078272

Hope it helps someone

@TON-RIJNAARD
To test things, you need

1. Device 1 with rf24L01+ radio

• Load "gatewayserial" sketch

1. Device 2 with rf24l01+ radio

• Load motion sketch, but add a line before
  #include <MySensors.h>
  so that it looks like this
  #define MY_NODE_ID 1
  #include <MySensors.h>

Switch on both devices and look at the serial messages from Device 1 (Gateway), When movement is detected, you will see new messages etc

Does this mean we can now have a multiple sensor LoRa network with secure 2 way communications and error detection/re-transmit?
Would really like to see a working example of this - no need for repeaters!

Check that the line you added ( #define MY_NODE_ID 1 ) is before #include <MySensors.h>
I found that you really need to add the capacitors. If you don't do this, try powering the UNO board separately via its power jack (in addition to the USB being plugged in)

If you're using an ESP8266 and you find it "SOFT WDT resetting" whenever a node tries to send a message, try moving the wire from GPIO4 to GPIO5 - There are a few esp12E boards which have been incorrectly screen printed - worked for me with this board!
https://twitter.com/bdcatalin/status/663434209265078272

-----*removed and put comments above

@TON-RIJNAARD
To test things, you need

1. Device 1 with rf24L01+ radio

• Load "gatewayserial" sketch

1. Device 2 with rf24l01+ radio

• Load motion sketch, but add a line before
  #include <MySensors.h>
  so that it looks like this
  #define MY_NODE_ID 1
  #include <MySensors.h>

Switch on both devices and look at the serial messages from Device 1 (Gateway), When movement is detected, you will see new messages etc

SUCCESS! - My "ESP8266 MQTT gateway" sketch now works OK - no need for a 3rd device
*EDIT I've been using this board and the problem is ....

I'M USING THE BOARD PICTURED BELOW AND THE LABELS FOR GPIO4 and GPIO5 ARE THE WRONG WAY ROUND (screen print error)

I swapped the cable from the header pin marked GPIO4 to GPIO5 and everything worked fine. I'm wondering if this is the same solution for a lot of people here (I've put this info on build page)
https://github.com/esp8266/Arduino/issues/437
https://twitter.com/bdcatalin/status/663434209265078272

Hope it helps someone

Not sure what happened before (!)
Just to say I still get this problem - I'm not sure if solved or not - so posting some device configurations for people to try .

I found that in situations 1 and 2, the ESP8266 always resets with WDT when the node tries to send a message.(before a message is sent, the ESP8266 is fine - it just waits).
Situation 3 works! - It would be good if someone can confirm if Situation 3 is the intended design ( I also tried uncommenting the LED lines - no difference seen) .

• Situation 1 (Does not work ) - 2 devices (Both devices have capacitors added and good power)
  Device 1 - Sensor node (Uno with motion sensor - added extra line for device ID)
  Device 2 - Gateway (ESP8266 using the "ESP8266 MQTT Gateway" sketch - No changes to code).

• Situation 2 (Does not work ) - 2 devices (Both devices have capacitors added and good power)
  Device 1 - Sensor node (Uno with motion sensor - added extra line for device ID)
  Device 2 - Gateway (ESP8266 using the "gatewayserial" sketch) - No changes to code).

• Situation 3 - (works! ) As above, but with a 3rd device
  Device 3 - Gateway (Uno with "GatewaySerial" sketch - No change to code

removed

@update
OK - just following this up with extra info.
Previously, I was using radios without the cap.
Once a 47 uf cap was added, I didn't need the extra power supplies (the USB power was enough to the Uno clones).
Thinking about this now, It wasn't the uno boards, it must have been noise/weak power on my laptop USB.

Also, I wasted a lot of time on a bad rf24L01 board ( I think I bust it a while ago by supplying 5v ).
So, the moral of the story?

• If you get a message saying "radio bad" - try another rf24l01
• ALWAYS add a capacitor to every rf2401 board