That comms issue happens due the terminal servers are crashing due some old persistent paths(network shares) in the customer's environment variables.

Please check the environment variables PATH and check if there is no network shares or old persistent paths which isn't accessible anymore, if it is there, please remove and restart the VDAs.

Desktop machines are showing in DaaS as unregistered. After restarting them it goes to registered but when end users are trying to launch the session or the application of the targeted VDA it goes into unregister state and it breaks the comms where neither via RDP is able to access it anymore.