You mentioned that you configured the watch to only collect time in AFib and not to alert when it starts, is that correct? If so how could you an idea of the time in AFib?

As I mentioned in a different post I don't think these devices are literally constantly monitoring for events but looking back at a previous period which for my Fitbit seems to be 10 minute periods.

These devices are still labeled as "consumer grade" and not "medical grade" they are far from perfect no matter the advertising. Example is the stair count feature. I have a set of stairs leading from basement to 1st floor that has 12 steps. I do those stairs literally 8 + trips a day. On most days it records "one" flight on many others "0".

If it can't count stairs I would not put a lot of faith in counting time in AFib.