Volume indicator keeps flashing on the screen while apps are open on my iPhone

The volume indicator on the left side of my screen flashes continuously when apps are open. The buttons aren’t stuck and work well. I’ve noticed the volume up button seems to be the action it's triggering. When I turn the volume down during the issue, it automatically goes back up. I have the latest software update (iOS 18.4.1).

I’ve used a pick to clean around the buttons — nothing was there — and I also used compressed air to blow them out. I’ve even factory reset the phone. I noticed the problem started happening two updates ago. It only happens when random apps are open, so I’m leaning toward a software problem.

The glass screen protector is currently broken, but a new one is on the way. The issue was happening even before the screen cracked.

[Re-Titled by Moderator]