Bluetooth connected but audio coming from phone

My iPhone 8 has started occasionally connecting to an audio device, but then the audio still comes out of the phone and there is no option in the airplay settings to switch the output device.

It first occurred with some cheap Bluetooth earphones and restarting my phone and re-pairing them fixed it for a while, but it keeps happening and has now started happening with my car.

My phone is up to date, I can see there have been a few people with the same issue, but not many. Is there a way to fix this permanently? I use Bluetooth audio a lot so this is a bit of an issue for me.

Thanks in advance