I tested most recent release with several ESP8266 modules. Afer rebuilding firmwares and flashing they either don’t boot up / boot with errors and crash after several seconds / periodically disconnect from local MQTT server (very strange). Downgraded to 2.13.0 and everything is fine.
I’ve run into some issues with the AWS-IOT, but it was something related to the certificate.
Try adding the debug flag “mos config-set debug.level=3” into the mos console. Maybe that will give you a better insight of what is going on.