How to restart SMB client on macOS Catalina? (Finder not connecting to shares)
I had the same problem, solved it by launching Activity Monitor and stopping netbiosd process, it gets restarted and then the connections started working immediately.
It's possible that I also stopped NetAuthSysAgent process as well, so if it doesn't work for you with the netbiosd process only, try stopping NetAuthSysAgent as well.