I'm having the exact same issue.
I can manually browse to the server by name or IP address, but it's not showing up automatically in network discovery. I pinned it to Quick Access and I can access the structure fine, but it does not show up whatsoever under Network.
Hard to pin down when it started as this week I've done updates to both Unraid and Windows.
No issues with ACLs on the Unraid server's folders.