Yesterday we were told by one of the offices/networks we manage that client PCs were unable to see mapped drives when they browsed to "Computer" on their Windows 7 workstations. The office is running Windows Server 2012 R2 Standard with the Essentials role enabled. Clients affected were all running Windows 7 Pro. All clients were affected.
When we tested the issue, we noted that Group Policy and Login Scripts (some users are getting their mapping via GP and some via login scripts in AD) were mapping the drives correctly, When we'd browse to "Computer" or Explorer on the workstations, the drives are initially there. But, if you wait long enough, the drives would disappear and neither local or network drives would be discoverable. If you restart the explorer process, everything came back. We could easily recreate the issue by browsing a network share and going around 4 folders deep and then back-out of the folders, returning to the root of "computer" ...where we should see all local and network drives. This would consistently "break" explorer and recreate the issue. Explorer would essentially spin and stop discovering any and all local or mapped drives until the Explorer process was restarted.
We examined the server and all expected services were running and the behavior was not manifesting itself on the console. Moreover, even when Explorer was not performing properly on the workstations, access to shares via UNC remained unbroken and quick. Likewise, users who had created shortcuts to mapped drives, were still able to browse server shares via their shortcuts. However, searches were either not working or painfully slow. No errors or issues noted on the LAN switches. Their VoIP phones also remained unaffected, as did their firewall.
We looked for commonalities on the workstations such as specific Antivirus definition files or Windows updates, but found no such correlations.
Out of ideas, we ran DCDIAG from an elevated command prompt on the Server 2012 R2 server and it passed all but one test related to a system log. It did not seem related. Later that day, we restarted the server and the issue subsided. The workstations were again able to browse mapped drives and shares without Explorer bombing out.
So... what happened here? Could this have potentially been some type of corrupt server "Network Discovery" service issue that the client workstations rely on? We knew it had to be top-down / domain-workstation based because of the way it was manifesting, but couldn't put our finger on what services to restart or begin to troubleshoot.
Nothing of consequence was logged in Event Viewer.