iPhone 12 Pro with suspicious symptoms ends being a swollen battery
The battery life was getting really bad—apps were sluggish and stuttering—and it would randomly die somewhere around 15%. The audio would cut out from speaker to "phone call audio" when I'd put it down, bump it, get notifications (in hindsight this was probably the vibration) and I'd have to force close the app I was using to get the audio back. If I left it it would slowly fade back to full volume.
Anyway, as we were talking about this I mentioned that the back glass is shattered and I've already had it replaced once (thanks, iPhone 12) and took the case off to show how bad the shatter is. (It's bad, trust me.) It was then I noticed my screen was not fully attached to my phone.
Everything works again!!
Patience!! Be SUPER patient and cautions at every step. Go slow with popping the screen off. Use steady even pressure.
Scrape the glue off the edges and then go in on it with the highest percentage of isopropyl alcohol you can get your hands on. I used 99% and it worked great!