I have an almost identical issue with me ESP MQTT gateway no longer connecting to nodes. Similar issues to start with in that it was good for a number of months then would stop, restart ok, then multiple restarts to begin working. I have now resorted to changing out the 24RF01 module and the ESP to try and locate the issue. Will let you know how I get on.

@eiten Ran into the same error but of course the community is always at hand, ready to help! Great! I'm using MySensors 2.3.2 release version. Downgrading the ESP8266 board library to 2.7.4 as suggested by @OldSurferDude did the trick. I'm still clinging to MySensors. So simple and inexpensive to use! All sensors and other stuff connects over three MQTT GW in three locations back to my Home Assistant. PS: Get well soon! Regards, Gunnar