I found an old HTC One (M7 I think?) thread over on Android Central that seemed to be discussing the same issue:
but no solution was found and it sounds like most people there just sort of gave up.
Sorry for the long explanation but one thing I wanted to try was using a ROM with a different bluetooth stack or system to see if that might point me to an HTC software issue vs a strict hardware issue. Does anyone have any recommendations? I'm fairly comfortable with installing ROMs though on my old Droid, Safestrap certainly made it easier for me.