Bro, the same thing occurred on my dads civic, problem started the very second day. It got stuck on aux, and then nothing short of disconnecting the battery shuts down the navig system. Same issue, even after you take put the key, and lock the car. And yes you're right, he also narrowed down the issue to Bluetooth (with iPhone). And same band aid fix, keep resetting or switching off the BT.
However, my civic is slightly newer than my dad's (his got delivered in mid April, mine got delivered about a month ago). I have been constantly using the Bluetooth and everything, mashAllah never had any issue of hangups, not responding etc. My phone is an HTC.
There is a fix for the hangups. Haven't tried it yet myself, but you could look into it. Search for the 9th gen fan club, gp to the posts from the past one week, you ll find a fellow pw member discussing about the fix.
Sent from my HTC Sensation XE with Beats Audio Z715e using PW Forums mobile app