Sadly, I don't have another BT device handy. I might buy one if I can find a pair of BT eadbuds I think are great, but that'd be buying something for potentially no reason and I'm skeptical.
Probably will anyway.
I can't say I've ever factory reset the phone. Think I should?
It may help, but you have to set it back up again. You can use smart switch on your computer to backup apps, files, settings, etc. It works well but you'll just have to sign back in to all your apps. May be worth a shot, but not 100% sure if it'll help.