FEC-100 Turns off on its own

The usual reply here, and correct, is call CS customer service, they are great and will walk you through diagnosis and recommend a solution.

Not sure why your FEC is stopping but I recommend the use of a remote thermometer to avoid that kind of situation of an interrupted cook.  It wakes my wife up who then wakes me up.  I've also had problems with remote thermometers losing sync and alarming at various times throughout the night, also wakes up my wife often so not so good.   I've found a Thermoworks long range thermometer and it works great and has 4 inputs.   I have my FEC in a steel building and it never loses sync.  Might let you sleep easier.

Intermittent issues are always the most difficult to figure out. The first thing I would do is put something on the same circuit that if there is a power outage has a display that blinks. This is let you know whether or not it is a power problem.