In the time I’ve been a user, I’ve noticed that the estimated pending BAT fluctuates (I’ve noticed it more on my Android, but a few times on desktop). I don’t watch it very closely, but the times I have noticed a loss in BAT estimates, the last “high” amount I could recall was always returned the next time I fired up the browser.
There is a flurry of posting right now about this issue. I think it has to do with a a few things: one is it’s a week out from payout, the other is something I read in another thread regarding this issue:
Of course, it could be something else, but maybe just give it some time. Support may pop in, or a more experienced user may offer other advice, too.