Activity Gaps

I’m looking for ideas/explanations concerning “missing activity*.
Example: Event history shows person A ascending stairs. An hour later, the next event is person A ascending the stairs again.

Missing is person A descending stairs, the only path down. Camera has CamPlus, though in this case, it should not matter as person A’s descent was >5 min after ascent.

Other example is Event showing person B crossing camera field right to left, existing bedroom. No subsequent event recorded of person B’s [known] return.