Assuming you are spending at least 20 sec watching the ad, then try to clear data → cache, cookies, etc.
And close this thread if it solves your issue,
So, we move to the ultimate then.
withdraw all your BAT to uphold and transfer all the crypto to other wallets. Now save your bookmarks, etc
And now uninstall it completely and clear system cache, TEMP DIRs, etc then reinstall.
NOTE: Do this only if uphold wallet is linked to brave at most 3 times.