Erin Stellato troubleshoots a cumulative update installation problem:
The initial email didn’t have a lot of details, so I started asking questions to understand what version was being installed, the environment configuration, etc. Turns out this was a two-node Windows Server Failover Cluster (WSFC) with multiple SQL Server 2012 instances installed, and one of the instances was still running on the node this person was trying to patch. To be clear, the two nodes were SRV1 and SRV2, and the instances were PROD-A and PROD-B running on SRV1, and PROD-C which was running on SRV2. This person was trying to install the cumulative update on SRV2.
The behavior Erin describes is a little bit crazy, but at least there’s a good explanation and way to solve the issue.