Is Service Pack 2 completely installed on Passive Node of SQL Server 2012 Instance?
The logs led us to review our Cluster services:

There was an error to lookup cluster resources. Error: There was a failure to call cluster code from a provider. Exception message: Generic failure . Status code: 4104. Description: .
HResult : 0x86d80014
FacilityCode : 1752 (6d8)
ErrorCode : 20 (0014)
Data:
    errorMessage = There was a failure to call cluster code from a provider. Exception message: Generic failure . Status code: 4104. Description: .


We determined that the replication agent service was the cause of the incomplete installation. 

We removed the service from Cluster Resources and re-applied SP2 without success. We stopped the service on the node and re-applied SP2 without success.  

Error: Failed to run patch request for instance: MSSQLSERVER (exit code: -2032664552)


We uninstalled the service from the server nodes, and then successfully "re-applied" SP2.

Follow-up actions: 


We'll be contacting the replication agent vendor to discuss why this
was required.
Review the Microsoft document "Patching SQL Server Failover Cluster Instances with Cluster-Aware Updating (CAU)", available here, which I discovered today.