@fair Which phone is this?
This is usually an issue with media playback that doesn't use media hub such as webapps. I guess Waydroid has the same problem, when you lock the device, apps get suspended. Interesting that Waydroid is also affected considering that it doesn't really suspend. I assume your phone has proper deep sleep so apps don't just suspend, the device goes into low power mode that processes like Waydroid can't function properly anymore.