Long story short, T-Mobile phone support doesn't have a clue. My wife's phone was a Galaxy s6 Edge plus. For what ever reason (that Tmobile SWORE was a phone problem), it constantly factory reset itself for no reason. We fought with them and they finally sent us out a different phone, the Galaxy S7 Edge.
That lasted a Week. It factory reset and she lost all her data. We started backing it up and it factory reset another 3 times for no reason. It finally stopped factory resetting itself an then the phone was damaged. Cracked screen but nothing major.
About 3 or 4 months after that incident, it started factory resetting again. Mind you, we now have identical phones and mine has had no issues what so ever.
We called Tmobile and they said "it has to be the phone, it can't be your account". Well, we spent the $175 to get a refirb unit from insurance, and it went through all the updates without issues...
And in the past 24 hours it has factory wiped itself 2 more times. It's a crap shoot when she opens her phone if it'll be factory reset or usable. This is a big issue since my wife has medical issues and this is her only line to contact someone. No home phone.
So, how do I troubleshoot this issue more since Tmobile seems unwilling to admit that the phone can be factory reset from their end? As an example of how ridiculous this is: The phone factory reset and I went through the prompts to the point where it was asking for her password. I let it sit since she wasn't asleep. I checked back a few times it was always at the password screen asking to go forward. Then when she wakes up and we're ready to continue, it is back to the welcome screen.
She put the information in the phone a few days just to dial out. Didn't do anything else, no apps, nothing. Then this morning when we look at it, it's back to a welcome screen. This is 2 different models, 3 physically different phones. Being an IT tech, the troubleshooting on my side is exhausted. The only possible last thing I can do is put a different Gmail account on her phone so it has no apps, and test it that way. But that is the only thing that has been the same on all 3 phones.