I found out what happened to my Brave Rewards.
Sometime earlier this year (in January or February), I enabled a Windows 10 feature called Focus Assist. For those not aware, this feature disables any notifications from popping up from any app on your computer (unless you specifically configure that app as high priority). And since Brave Rewards ads show up as notifications, I never saw the notifications.
I had configured Focus Assist to automatically turn on at night and off in the morning so my PC wouldn't unexpectedly make loud noises in the late/early hours. So when I manually enabled Focus Assist I assumed that, like Android's Do Not Disturb feature, it would automatically disable itself at the scheduled time in the morning to deactivate the feature. I was wrong. So I've unwittingly had Focus Assist enabled for most of this year. I noticed it was enabled and manually disabled it a couple weeks ago, hence Brave Rewards starting to work again briefly. But then I re-enabled Focus Assist during Ludum Dare 46
so I wouldn't be disturbed and so my screenlapse wouldn't capture any notifications containing private/personal information.
I've disabled Focus Assist yet again and have already seen 2 Brave Rewards notifications. So all is well on that front.
As for the regular ads all over the place I complained about a week ago, including YouTube, Brave recently had a buggy/bad adblocking filter
that got pushed out which caused ads to fail to be blocked for virtually all Brave users. It has since been fixed.