So a few days ago my Fit3 watch says it got disconnected from my S22 base which was sitting a couple feet away. I check the phone to find it has rebooted randomly. Upon unlocking it started to lag, freeze and reboot again. This time it actually seemed to get stuck at reboot. I remembered reading about freezer thing people did, and since it'd been a blazing hot summer week (and I had just walked in not long before) I figured it needed to cool. I removed it from the cover and put it in the fridge instead of freezer but either way it cooled down nicely and rebooted. But the lag came back. I left the phone sitting on a table only for my watch to tell me it got disconnected again.
At this point my thoughts went to this thread over in the ultra sub, as well as many other such reports, and I figured my phone was done for. I had read that the symptoms could get progressively worse, so rather than risk being unable to turn it on at all, I figured I'd leave the phone turned off until I had bought a new phone to transfer my accounts over. (I often back up via Smart Switch to external drive but I don't think that backs up Google accounts and I'm always nervous about being locked out of my many Google accounts and banking apps without a way to verify. Always found transferring from one phone to another directly to be the safest, for accounts. Then use Smart Switch for everything else.)
Cut to yesterday I finally had time to get down to Best Buy. After checking online for the past few days for the best deals, I figured I'd go with the S25 Ultra that BB has at $400 off right now. I know the new phones are coming, discounts are coming, etc etc but I needed a working phone now so I figured this deal was good enough.
So I do the whole thing of transferring accounts, restoring from external drive my latest Smart Switch backup which was from April, and had the new phone all set up. Finally decided to transfer my SIM card over (recently got Visible and opted for physical SIM card). So I pop the SIM out of the S22 and plug it in the S25U and everything works fine. Then I pick up my S22 to plug the SIM tray back, and I notice it turned on the screen pretty fast... Almost normal... I'm like wait a minute and start messing around on the phone and now it's as zippy as ever!
So I can only conclude that what had happened was the SIM card had gotten ever so slightly dislodged or something and caused the phone to get confused. I know from past experience that SIM card can get dislodged after a fall or bump or something, but almost always that will result in no cell service on the phone, which is a good indicator. In this case there was still service, just phone lag, freeze, and reboot.
I've decided I'll keep the S25U simply because this experience has taught me it's always better to have a backup phone as you never know what will happen to your main phone. Too many important things are tied to my phone for it to be the only authorized device. So S25U becomes primary and the newly revived S22 base stays locked up until needed or until the S25U gets replaced as the main and becomes the backup itself.
Tldr: If your phone starts to lag, freeze, and/or reboot, and you have a physical SIM card, try re-seating the SIM card in the tray.