If you can connect to some servers but not others on the same network, an expired certificate is the most likely culprit.

"Require user authentication... using Network Level Authentication (NLA)" Microsoft Learn 🌐 Network & Environment Checks Use IP instead of Hostname:

His own workstation was trying to connect to Lab 4, but Lab 4 was already in a session. A session started by its own operating system. A ghost session.

Overzealous local firewalls, corporate firewalls, or antivirus software may flag the RDP traffic as suspicious and terminate the connection.