Every now and again when using Bluetooth devices, changing the volume completely switches off my my custom equaliser. It's extremely noticeable and makes music sound significantly worse. This can be fixed by turning the display off and back on and then changing the volume - it then goes back to my custom equaliser properly.
Not sure why this is happening. I'm on an S21 on One UI 4.0.
Any app that plays audio, YouTube, Netflix, YT Music, Chrome, whatever it might be, so it's definitely an OS wide issue as opposed to an app. It's the built in equaliser in Settings > Sound and vibration > Sound quality and effects > Equaliser.
Like I said when it happens it basically just disables it. I haven't actually checked what it says in the settings there when it happens, I'll do that next time it does though. Just turning the display off and back on then changing volume brings it all back.