[AC Question]

for no apparent reason and restarts frequently on its own. How do I fix this?

When this happens I will get a message on the phone stating "bloothtooth shutdown unexpectedly"

[B. Diddy]

Welcome to Android Central! Try booting into Safe Mode, to see if it's a 3rd party app that might be causing the instability: https://support.t-mobile.com/docs/DOC-21007