We have now tried with updated driver for the video card. It did not help.
We then changed the minimum allowed allocated video memory in BIOS. It was set to 32 MB, we increased to 512 MB.
However, the figures of avaliable memory for the video card in Windows 10 is very confusing, windows states serveral different values depending on where you look (device manager adapter settings, task manager Performance GPU Memory), ranging from 128MB to serveral GB avaliable video memory so I really can't tell how much video memory we actually have.
The BIOS setting 32MB --> 512MB seems to have made a difference. The error message "Ext. E-Stop Triggered" does not seem to appear as often. We will however need a weeks production to be certain. The equipment runs at about 8-16h / daily Mon-fri so there is a great chance we will see the error when it occurs.