Hi, Administrator,
BV9500 2018101619ROM.
During using FM radio, after passing some time, FM radio become stopping when screen off. Not using any battery management apps. FM radio app does not appear in pre installed battery optimization settings.After rebooting, it come back to normal.

Please guide to prevent above phenomena.
If it is ROM issue, please reflect it in next update.
Thnaks in advance,

Can anybody else confirm such issue? 

I tried, the phone was playing radio, locked and unlocked the screen, waited until the screen turn off automatically. The issue didn't reproduce. More detailed data would be needed. Like after what amount of time the radio went off.

Azarashi try to perform a factory reset and report back.