I've managed to solve it for you A20 M20 users out there. Turn off auto control in your game booster settings (accessible while in a game)

Samsung customer support, it is not an accessory problem, its the built in program in the device. The feature where it lowers the volume during games, signaled by a "pulsing" line on the edge of the screen. Any way to turn it off and keep the volume ...

This is an annoying feature of samsung which also happens on my M20. The volume gets lowered on games signaled by a blue line by the edge of your screen. MANDATORY FORCED Volume lowering for the "performance" of the phone while playing games. This ha...