Black screen on guest upon connection

Hi there, first post here.. did a search but haven't found a solution.

I'm facing this situation: a customer of mine needs to let some external consultants to his pc.. all of them are using TV

the customer needs to see what's going on on his screen, but since 15 days he can't.. when the remote pc connects, the screen goes black

local O.S. is windows10 pro 64 bit

we tried:
- to use the quicksupport TV already downloaded: not working
- download the last quicksupport exe: not working
- install TV from v11 to v13 (removing the old one before installing the new one and rebooting pc): not working

there's no active RDP session while the test were done 

We suspect that one of the last windows update broke something but we weren't able to find exactly which one.

any hint?

TIA