I have no suggestions, but can confirm in the last few days I have seen this behaviour a few times on one of my cameras. Normal, motion triggered event, followed shortly afterwards by a short video of nothing. This is only on one of my cameras, and it just now it gave me a low battery alarm, which I’ve never seen before. My other battery changes have all been preceded by some sort of misbehaviour, before ever showing low battery, so this is a first for me.
I’m going to change the batteries now, and see if the odd behaviour persists. I will keep you posted.
Doubt it’s your issue, seeing as you have several cameras showing the same issue, but mine need changing anyway, and it seems to be only one of my cameras.