Sounds like you’ve possibly got water damage. I’d get it checked out. You may have to replace it if there is

I’d swim with it but I wouldn’t take in a sauna. Don’t think it’s wise to do so tbh

Ehh, I’d rather go with a 13PM but your call

Tbh, having the screen on the entire time the phone was on charge wouldn’t help. You probably have StandBy set to never turn off the screen. If that’s your personal preference then you may run into this issue often

Personally, all the cases I’ve tried for my S8 have been bad so I just go without it now. Remove this, it looks really off