Constantly restarting after prolong use

I don't know very much about these phones, but I have two guesses.

1) It's possible that even though the phones are identical, and even if you may have bought them at the same time, the firmware may be different, check the firmware version on both phones. It may be that an older version is set to shut off the phone at 32C.

2) Thermal expansion is causing a faulty connection somewhere within the phone. This is probably only likely if your wife's phone was at some point subjected to either hotter or colder than normal temperatures, causing a loose connection that doesn't cause problems at normal temperature, but once hot, is disconnected. If it's this, I have no idea what to tell you to do. Try getting it replaced from the company perhaps? They might refurbish and re-sell it.

I don't know the answer but my EVO4 does the same.

I think it's related to processor temp instead of battery temp.

It resets after using any app that runs the processor hard for 10 to 15 minutes. Makes it useless for watching videos or playing games, but seems to work ok as a phone. The batt temp usually shows around 105 to 107F when it resets.

It also occurs if left in a warm area like a parked car.

I can trade it in in Nov so that's probably how I'll fix it. LOL