Before seeing your comment, I went ahead and installed 21.3.2160.7699. Issue still still but previous workaround (Restart session manager service) mitigate the issue for some time.

We are using 
21.2.2159.7699

On premise - WIndows server 2019

I see a new update 21.3.2160.7699 this morning... will that help ?

We found out that restarting the Session Manager service on the Screenconnect host server mitigate the problem, for some time. After that we are able to update guests but eventually, it fails again. We had to restart the Session manager (which restarts all services) 4 to 5 times to get through.

Somehow, the updater queue is stuck when it encounters a specific unknown condition. 

@Rishikesh Gajul : Any updates on this ? 

Same here updates are stalled. 2/3 of Unattended got updated though

on the latest 21.2.2159.7699 release

Same issue here. When the DP monitor(s) are powered off, CW Control does not render screen correctly. Grey screen. Been seeing that for quite some times now. I can relate now that the cause is monitors being powered off.

Inputs are sent to guest (login info) then desktop appears once, with wrong resolution.

Lenovo ThinkStation P520c with high end P2000 Nvidia Cards (no "consumer" driver involved here)

Workaround : using RDP or backstage mode for maintenance. (a real fix need to be provided as this issue is major for SC)