I think I found the answer to my own question.
Partial connection - Connection that exists in the Firewall Connections Table, but not in the SecureXL Connections Table (versions R70 and above).
- In Cluster HA - partial connections are offloaded when member becomes Active
This is found in SK98348 Best Practices - Security Gateway Performance. I interpret this to mean that PXL connections are moved to SXL connections upon fail-over to maintain connection state.
We just inadvertently ran into this as we were moving tens of TB of data and the connection eventually caused the gateway to run out of memory and fail-over (all 24 GB).
From testing last week, we were able to figure out how to keep this connection out of the App Control blade, thanks to posts from Tim in the PXL Medium path thread. We are still working on the Threat Prevention blade yet for exclusion as this blade still causes the connection to drop to PXL. We still have a few things to try yet.
As a side note, our memory issue is probably because of running old Jumbo 216. I see they fixed some issues in the newer versions for App Control with memory usage. The memory issue is not present if the connection is running SXL path.