I have not seen this happen with shadows.
I would...
Check video drivers are up to date.
Check how much free RAM yo have.
Check how much free space you have on your local hard drive.
And make sure Archicad is up to date.
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