NINA won't park the mount in response to reaching the meridian or being unable to flip, though. From NINA's point of view, parking the mount is an explicit, not implicit, instruction - NINA will do it only if it has reached a point in the sequence where a Park instruction is the next thing to do, or if you press the Park button in NINA's telescope control area.

As Ray noted, there are few configurations in APCC that can cause the mount to park - reaching a horizon or meridian limit, or the CP watchdog's loss of contact with APCC. Since this seems to involve being at or near the meridian, I'm inclined to think you're not flipping before reaching the meridian limit you've defined for the mount, and your "Action when limit reached" setting is "Park". A violation of the meridian (or horizon) limits will also be indicated in the Telescope Position area of APCC, with the Meridian block blinking yellow.