Screen displayed multiple times

[frit]

Booting from a Fujitsu as the client with an ASUS monitor works well, but when my client is a HP EliteDesk 800 G5 TWR with a Fujitsu PS19-1S as monitor, the screen is shown multiple times on the display and it seems that only every second line of pixels is printed.
Picture of the display: https://upload.picpaste.me/image/Ayihk

Booting the same image from a USB stick works fine.
I'm using a FOG server as server and a tower PC as client.
Could this behaviour be caused by a wrongly written PXE menu?
(Please let me know if the uploaded image isn't present any more.)