Still no solution until now.
Is this bug under your consideration??
We are having this issue only on 2 Windows 10 computers, I was researching for a fix and I reached here, even this post is 9 months old, we are running 20.11.1622.7619 version, I got that there is no solution or workaround when I checked in over chat (Ticket #14154912).
Each computer has 2 monitors
1- I tried to dig in and trying to fix the issue and I found that the issue is related to Display driver, Intel graphic, when I uninstalled the driver it worked.
2-Digging more into the display driver I found out that after decreasing the resolution below 1280x960 for the HDMI monitor, Blank Guest Monitor worked. However, they do flash to black quite a bit.
Still need a solution from @connectwise
Customer support service by UserEcho