Do you see any pattern? If it's totally random, then there might be a hardware error
It's not so simple. OnePlus version of Always On Display is an active screen that looks like AOD but it isn't and because if this, it draws more power. This is why it doesn't always stay on like a proper Always On Display. The downside with AOD is that it's not as feature rich as OnePlus ambient display. We feel it's more important with a watch that is always visible but it's ofc very subjective what is more important. Always on or more features?
It will ONLY vibrate if it doesn't recognize your finger so your issue is not the vibration but the fact that it doesn't recognize your finger. To fix this, please remove your current fingerprint. Make a new one where you make sure to press it from all possible directions and try to include partial fingerprints as well. You can also have multiple profiles for the same finger which will increase the accuracy even further.
In what way? Should we kill apps? From my experience, in 9 out of 10 cases when users have complained about battery life, it has been because of something the user did. Not intentionally. It could be an app they downloaded, some setting or whatever but not a bug in our system. We know from media that the ROG Phone 2 battery life is VERY good so it's not the system or hardware that's failing.
Why do you want to hear both? Isn't the call quality most important? I tried for fun what happens during an incoming call on some other phone brands and none of them played any game audio during a call.