Error when upgrading SQL 2016 to SP2 - "The given key was not present in the dictionary." I am trying to patch one node in a SQL Server 2016 Standard FCI.  I removed the node from the cluster, and ran the installer, but it failed.

The summary file contained the following exit code / message:

Exit code (Decimal):           -2146233079
Exit facility code:            19
Exit error code:               5385
Exit message:                  The given key was not present in the dictionary.


I cannot find anything obvious in the "Detail" file.

Can anyone recommend where I could go to get a clearer idea of what failed?
What I am understanding from your requirement to patch a sql clustered environment you are removing a node. This is definitely not the right way to proceed. You need to patch the current passive node first. Once everything goes well do a failover at node level. 

Now the patched passive node becomes active, do your health check for the patching done if all look green. Once ok, proceed with patching on current passive node. 

If there is any node preference you can failback to original active node and do health checks to ensure patching went well.