FWIW, I have an S8 and it's definitely not doing any of that.
I'm guessing that the "update" of which you speak is Android Pie. That was a major update; I'd guess that maybe 30% or more of the various settings on the phone moved around in all the menus and there's certainly a lot more settings that what there used to be.
I'm madly guessing at two, maybe three possibilities:
- You may have had some cool add-on that made your S8 look great under Oreo, but under Pie it's Messing With Settings. If you've got something like that, ditch it?
- There's a slew of detailed settings about the lock screen, security settings, and all that jazz buried in Settings->Lock Screen, and Settings->Biometrics and Security. I think that there's a way to set all the various parameters in there to Default, which may be a great place to start from. One second... Yep. Under Settings->General Management, there's a Reset function that puts everything to Square One. I've used that, it works, but had to reinstall some corporate apps after the fact.
- It's barely possible that you've managed to get OTA'd and somehow corrupted the install. I'd bet on #'s 1 or 2, above, but I suppose it's possible. In that case, flashing the phone to T-Mobile's official pie load using Samsung's Odin software will get you a clean install. XDA Developers has instructions; in fact, further up in the Android discussion group somebody put up a basic tutorial. Be careful lest you end up with a brick.
I haven't done anything to change the way my S8 changes in apps or backgrounds. I use what is already in the phone. So I dont think thats the problem. I tried your number 2 possibility but did not seem to work. I dont even want to try 3 to make it worse. I went to t-mobile and the employee said they are a lot of people having problems with sending and getting messages. Told me to just wait for a patch because my phone seemed normal. Thank you for the options you gave me to try and resolve this issue.