This issue is present in both the Remote Desktop App and the new Windows App. The frustrating thing is this used to work in earlier versions of RDC, and it works correctly in non-Microsoft clients like Parallels Client for MacOS.
The issue is with NLA (Network Level Authentication) when the remote PC is a domain member but is not on the domain network (for example connects remotely through VPN). If the machine is rebooted, you cannot connect to it without physically logging in first. Otherwise you get error 0x1807.
Steps to reproduce:
* Use PC that is part of a domain but is not connected to the domain network (guest wifi, VPN disconnected, etc).
* Reboot PC
* Attempt to connect with MacOS Remote Desktop or Windows App.
* Receive error 0x1807.
* Manually log in to PC, then attempt to connect.
* Connection works.