Hi
this is always an interesting one and there is an article somewhere that details how the process works re the max number of sponsored images in a day etc but I can’t put my hands on it. I know there are various maximums and things that kick in as a way of protecting the integrity of the rewards program. There was a thread a while back that I was on which gained an official solution which still left some confused but may give you some deeper understanding https://community.brave.com/t/sponsored-images-not-rewarded/305238
there is also the main page which has more info and a way of you checking things are working as intended https://support.brave.com/hc/en-us/categories/360001053052-Rewards
As I say in the thread above, it has never bothered me that the counter sometimes appears to stall as on nearly every reward payout I have recevied a high amount in BAT than was estimated on my browser so my guess is that the internals or some other system compensates for any other issues that occur.
Not sure this answers your issue as clearly as you might want but hopefully it gives you something to increase your understand of what’s happening.