I created a restore point, just in case something would go wrong. I then followed the procedure described by @avolanche by first turning updates back on, reinstalling the offending update (KB500802) and restarted. After restart the new patch KB5001649 was available as an optional extra quality update. I installed that and restarted. Now printing is back to normal, and I hope Microsoft found the solution this time. So thanks to avolanche for testing the new patch and reporting.
That was one computer OK. I've got one more desktop with 64 bit Win 10 Home and two laptops with Win 10 home 32 bit. I will now update and patch them and report the results. Hopefully there will be no problems.
I have now updated the remaining 3 computers, one desktop with 64 bit W10 and two laptops with 32 bit W10. All behaved in the same way. installing KB500802 caused the same print problem with most of the image missing. Installing KB5001649 brought printing back to normal.
I wonder how many were affected by the bad update? If it were everybody having a Windows 10 computer I would expect the forum to be flooded with posts about the problem. It looks like only a small percentage of Windows computers were affected. It seems the problem is independent of printer make and model and also of Windows language. But maybe it is dependent on the computers' hardware?
My computers are old, two had originally Windows 8 installed, one had Windows 7 and one had Windows Vista. All have Intel CPUs. I have attached a text file with some hardware details, collected by Speccy, a program to give some hard- and software details of computers.
Yes the Celeron laptop is the one i use for the V5204 Service tool. I used an Asus Eee notebook PC with Win XP to run the V4720 Service tool, but many newer printers have no XP drivers.
The Celeron laptop uses Windows Defender and each time I want to use the service tool I have a struggle with Windows Defender not to delete the tool, even if I have created an exception for the service tool.
BTW the locking of the service tool to the computer works. I once "stole" the WLAN card from the Celeron laptop to use it in the other laptop that had a defective WLAN card. After swapping the WLAN cards the service tool didnt work. After swapping the cards back the service tool worked again.