The zone history page gives you a log file of zone entries and exits.
When a tag is powered off (or when it can not get positioned) for 1 minute, it will be registered as a zone exit. When the tag is powered on (or when it can be positioned) again, it will be registered as a zone entry. 1 minute is the default time, but this can be tweaked by Pozyx engineers to better align with your use case.
Because there's hysteresis on the zone triggering, 1 position update is not enough to trigger a zone entry or exit. Which means that if a tag for whatever reason makes a quick jump outside of a zone, and almost directly goes back into the zone, this won't be reflected in the zone history log. This data smoothing can also be tweaked by Pozyx engineers to better align with your use case.