Average BNB balance decreased for no reason

Hello,

I have had 1.02 BNB in the BNB vault for more than 30 days. until a few days ago I was level 2 (average BNB greater than 1), but yesterday I saw that a payment received cashback of only 0.1%, and in fact binance says that my average 30 day BNB holdings are less than 1 (0.9917), so I'm considered level 1. Whyis that? I have not done any operations and my BNBs have always been in the BNB vault.

Any idea why this happened?

Thanks,

Cas