Without properly understanding the issue on the backup, we can't troubleshoot the issue well.
Still, I am thinking an option.
- Create a different VM within the same subnet with a similar internal IP range of the problematic VM
- Try RDP from the new VM, using internal IP (Make sure that there is no NSG rules set to block the RDP port 3389)
- If still RDP is not working, try accessing the the the VM's services, files etc. to see if something can indicate the problem
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