This seems to be a common occurrence here with BAT disappearing.
I restored my wallet to my browser and it showed all of my BAT available to me. I decided to link my wallet to Uphold to see if I could transfer some of it out since I have quite a bit saved up. After I linked my wallet to Uphold, it still showed all of my BAT in my wallet but nothing in Uphold. I thought that was weird, so I just left it for a few hours to see if some process on Uphold/Brave’s side would fix the issue.
After checking again a bit later, my wallet in Brave is at zero and there is nothing in Uphold. I tried restoring my wallet again to see if there was a bug or something, but it’s still sitting at zero BAT.