Ok, I think that this would be an easy install / test to see if it is an ArcGIS client issue or other issue.
You mention that it worked till May 6th. Besides Windows updates, you may need to reach out to your IT dept. to see what (if any) other network, database, VPN rules changed.
Where there any ArcGIS patches applied to the Server / Geodatabase?
What are the errors that you are receiving in the ArcMap when connecting?
--- George T.