As was shared before, when the browser recently updated it introduced a change. If an ad pays 0 BAT then it doesn’t increase the counter. They are setting it so that it only counts paid ads.
So those ads that “disappeared” in the update were the ones that paid nothing. And going forward it’s possible/probably you’ll see a lower count of ads since it’s not including the House Ads that pay nothing. You can see the Github where they implemented the change at https://github.com/brave/brave-core/pull/31019
Other times this has been asked and answered:
- Where are my BATs? October - #9 by Saoiray
- Brave rewards ads erased! - #6 by Saoiray
- Mismatch in rewards - #2 by Saoiray
- Missing rewards - New User - #3 by Saoiray
- Ad Count Decreasing After Reboot: Lost Ads Watched Record - #2 by Saoiray
- I had 244 ads viewed, but today I logged into Brave and it says I have 155 - #2 by Evan123
- I lost the ads that I see this month - #2 by Evan123
- Brave ads number is automatic decrease by total ads - #3 by Saoiray
- Ad Count Decreasing After Reboot: Lost Ads Watched Record - #2 by Saoiray
I really do suggest you try searching for existing topics before creating any in the future. As you can see, it gets old seeing people just rushing in to ask the same question and people having to repeat themselves over and over.