You gave the example of the relay actuator for the function but I took the esp8266 gateway to start with. What I mean is that you see "in the top" the spi.h and eeprom.h declarations. Then a number of #define statements. And just above the void setup()the MySensors.h and esp8266wifi.h are declared. I had some definitions that required the MySensors.h and those gave errors because they were declared below the "normal" position of the includes but above the "MySensors.h". (I even considered filing a bug ticket for the missing MySensors.h :) ) So I declared the MySensors.h in the top of the ino below spi.h and eeprom.h (because I had not seen the MySenors.h almost at the bottom of the ino). And then some errors were fixed and a few other arose. It took me quite some time to see that the MySensors.h was declared sooo low in the ino where I definitely had not expected it.

@martinhjelmare and @rollercontainer There are days that I feel less intelligent. ;) That mygateway1-in is indeed the reason and exactly as specified in the GatewayESP8266MQTTClient.ino sketch for incoming subscribe messages. mosquitto_pub -t 'mygateway1-in/15/1/2/0/2' -m 0 and mosquitto_pub -t 'mygateway1-in/15/1/2/0/2' -m 1 does switch the relay off and on. Thanks.

I saw a commit to the DEV repo so I did a git pull this morning, started arduino and recompiled and flashed. It's working. Immediately! The fixed ip-adress was there and the the serial monitor displayed nicely the debug and node messages. The mosquitto broker receives the info which I can see using the mosquitto_sub command. It beats me, as I can't imagine the yesterday evening commit fixed it, but I'm glad it works. For reference: This morning I used the 2.2.0 esp8266 board managers version.