iPhone XS Bluetooth changes devices erratically

[gsusser]

On my iPhone Xs, at times I'll be using one bluetooth device, i.e., a speaker, and bluetooth will stop working or switch to another device. Apple support had me do a factory reset, but no help. They told me to take it to a service center. Before spending a bundle, I'm hoping someone can point me in the right direction. I just posted about another iPhone problem and wonder if they're related -- the volume on the phone (as in telephone) is too low.
Thanks.

 

[now i see it]

First choice: Take to an Apple Store or mail it in.
Second choice: Authorized service center
Third choice: Unauthorized service center.

Be prepared that the repair estimate might not seem worth it... if it's repairable at all.