Do you have two or more zones overlapping each other (maybe even in layers that are turned off)?
Maybe the marker can't register what zone it belongs to because of the other zones until you edit that zone that is currently on screen.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11