I haven’t looked into the issue any further that when I last commented on the thread. I’ve been moving house and holding out for the Photon to see if that made a difference.
It looks like there area few users having similar issues like this one Code not stable
I thought after @baatsm 's post it might be related to MQTT but if @rpsmithii 's issue is the same then it’s probably not.
Also in response to the DHCP suggestions, even if it is related to DHCP the core shouldn’t reset or stop running user code for a long time if it needs to renew it’s DHCP lease.