If you have a S9/S9+ LED Case, don't upgrade to Pie.

[Steve Waring]

The case stops working as soon as you upgrade, and it does not even turn the screen off/on when you close/open the case. It's been reported to Samsung many times, it's reproducible (take the case off and put it on an Oreo phone and it starts working, reinstall Oreo and the case starts working), but Samsung do not appear to be doing anything about it, despite this being an expensive case.