You get the following error in the Windows Event log:
Event ID: 30804
Event Log: Microsoft-Windows-SmbClient/Connectivity
The network connection failed.
Error: The transport connection is now disconnected.
This indicates a problem with the underlying network or transport, such as with TCP/IP, and not with SMB. A firewall that blocks port 445 or 5445 can also cause this issue.
This is often because either there’s a network issue stopping the communication (as stipulated in the error guidance) or that the computer is too busy to accept the request (such as if there is a backup occuring that’s using all the resources).