I have an issue similar to this.
I connect via windows remote desktop to a windows server 2012 R2. On that machine I have virtual box installed and want to run my virtual machine. I don't want to connect directly to the VM via RDP. Just rdp to server and work on the server like on a local machine and working also includes running this VM. ( I don't even have the RDP extension installed)
My VM has virtual display disabled and installation of virtualbox did not break RDP connection. What breaks the connection is as soon as I start the VM. The VM uses NAT not bridged networking which also is slightly different from the linked thread.
So what causes my Remote desktop connection to fail on start of the VM? How can I work on the remote server with virtual box just like ti was a local PC without losing connection?
Issue most likely caused to running nested virtualization (see potential answer in comments or here). My solution was to just request another VM via IT which is a bit cumbersome usually.