I have 2 electrons running the same code for a while now and both suffered the same issue at various times. Basically i found the electron frozen/stuck with the LED flashing blue quickly (as it does when connecting) for days. They required a hard restart to get back going.
One of the units is running firmware 0.6.2 and the other 0.6.4 thinking it could be a firmware issue.
They are both running 3rd party 3G sim cards from Telstra. Because of this i am using Particle.keepAlive(60).
All the units are in areas with very good cellular signal strength and good power supplies.
In the code I have the units doing a hard restart at midnight everyday (System.sleep(SLEEP_MODE_DEEP, 10)) but the issue occurs at various times outside of this reset.
Any ideas or guidance as to what could cause the electron to freeze in the connection “phase”?