I only have 20 open at the moment but I drew a 300x600 mesh and I didn't have the half snap points either.
I drew a small slab and no snaps for that either.
Until I turned the snap guides off and then back on again.
Seems it got stuck somehow.
Now when I close and re-open Archicad it works straight away.
Just checked 21 and that was fine as well.
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