You have learned so much young padiwon (sp?)Less likely, but it could also be possible that you return pump in fluctuating. (Failing?)
My previous pump was doing this on my
Big tank before I replaced it. So if the ATO fills to the correct level and then subsequently, your return slows down, it could appear to be overfilling.
Again, usually the less complicated explanation is more likely. Just a random thought I had.