Welcome to the community forum 
A number of problems with Bluetooth have been reported following the A15 update, including by some hearing aid users. The main “FP4 A15 complaints” thread is here, but that’s a long thread and mostly not pertinent to your problem.
A thread on audio here.
A similar problem was reported for the FP5 in the spring.
I think it’s important that you report your problem to official support