Things that run on their own schedule without you needing to intervene – like if one of your AnkiHub-related add-ons syncs its updates periodically in the background.
Okay, you win. I don’t get any prizes for convincing you that’s what the issue is, and if you’re not interested in trying my suggestions, you don’t have to.
I guess you should start comparing Card Info between devices and checking Card Modified and Note Modified timestamps against review times [see the links for suggestions I’ve given to other folks who also didn’t believe me]. When you come up with a set of steps to consistently reproduce this issue – let us know.
I don’t get any prizes for convincing you that’s what the issue is, and if you’re not interested in trying my suggestions, you don’t have to.