I'm not sure if there's an easy way to pinpoint a hardware issue. One thing to try first is to boot into Safe Mode and see if any of these problems happen then. If they don't, then some 3rd party app you installed might be causing the instability. I know you did a factory rest already, but if you immediately reinstalled all of your usual apps, the offending app might still be there causing problems.
https://support.t-mobile.com/docs/DOC-28997
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