Windows server 2025 SQL patching cluster problem.
Dear Team, I have a problem when I am patching upgrade windows server 2025 with KB5091157. After patching is the clustering is not able to join back; it shows the error with credentials. The log error is "Cannot connect sqlxxxxxxx." you do not have administrative privileges on the cluster. Contact your network administrator to request access. Note: The server is not in a different VLAN network.
SQL Server FCI CSV storage flips multiple times into Online (No Access) state and eventually fails
Dear Team, I'm encountering an issue with our SQL Server multi‑instance failover cluster after applying the OS security patches and restarting the second node. Once the second node comes back online, the Cluster Shared Volume (CSV) briefly flips multiple times into Online (No Access) state and eventually fails.(we can make it online manually, but again flips and failed after sometime). To make the SQL cluster available, we either need to shut down the VM or revert the patch. Before the patching, all cluster roles and SQL instances were moved off the node, and the cluster appeared healthy. The issue only occurs after the reboot of the second node. (first node patched and restarted and everything working fine) OS : Windows Server 2025 Standard Patch tried: KB5075899 (February,2026 ) KB5078740 (March,2026) KB5082063 (April 2026 ) KB5087539 (May 2026) Could you please advise if there are any specific checks or steps we should follow during OS patching to prevent CSV access loss? Is it an issue with the patch or something else? Any insights or recommended actions would be really helpful to perform the security OS patch in the server Thanks you!