I did a factory reset on my s9+ yesterday, and after that when i try to search for updates it tries to register my phone, but it fails everytime or just keeps trying forever. Idk what happened everything worked before doing a factory reset, i'm using the same sim card too if that can be a problem. It just won't let me check for any updates. It's an unlocked s9+ running on android 9.
Be sure you have Samsung account inserted as Default and try again my friend. But it's a inusual problem that is not know for me until now.
I undestund that you are refereing about system updates and not googles app updates.
S9+ is under warranty, do not discard to use it to set phone as default with update capacity
Could be some own keys lost from inside code, let Samsung to speak but today I can not to see anyone for here after a few hours, will be entertained in something more important of course, such as bans or other hot topics