I've a test Remote Desktop deployment that is failing to be managed via Server Admin. Collections and deployment overview never stops refreshing, but nothing is shown:

When I try to edit deployment details, another error shows:

Everything is working properly from users side, as they can connect and work. I also can manage all deployment details and even create new applications through PowerShell and New-RDRemoteApp command, but the only failing related command is Get-RDUserSession.

I see nothing strange in event logs that may give a clue, so any help is very welcome.
Kind regards.