Hey, my 5X did the exact same thing. I couldn't find anything on the web about it happening to anyone else. I thought it was just me.
The thing died on my desk at work, wouldn't even turn on, just a few days before I was going on a long trip so after a few hours of looking for fixes and talking to support I just went to an Apple store and got an iPhone. Now I at least feel comfortable that if I have an issue I can go to a physical store and get help in a pinch.
I had the 5 as well that constantly boot loaded. A couple years later I really wanted the photos off it that hadn’t been synced and so I took it apart and found the issue to be a design flaw in the power button. I made a custom power button replacement and it booted right up. I have no idea who’s idea it was to have the entire phone’s functionality dependent on a thin, flimsy piece of plastic, but it made me never buy a google product again. I had a google pixel 2 at the time and it’s the last google phone I’ve had.
The thing died on my desk at work, wouldn't even turn on, just a few days before I was going on a long trip so after a few hours of looking for fixes and talking to support I just went to an Apple store and got an iPhone. Now I at least feel comfortable that if I have an issue I can go to a physical store and get help in a pinch.