I have a different phone (pixel 2) with the similar issues. Still very unreliable android 9 BT implementation. What works for me is to change bluetooth AVRCP protocol version In developers settings and restart the phone. No matter the version, in seems like the change sitelf clears some garbage. Then everything connects for a while. But you have to change it occassionaly to fix it. Total shame on google developers to produce such.
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