Rosetta Net Process Model Not Initiating

I am receiving a PIP 3A6 document from one of our Trading Partners. The document is recognized correctly inside of TN, and a conversation ID is being generated. My process model subscribes to the TN document that is being persisted, but the process does not get initiated.

Does anybody know what could be keeping my process from being initiated?

I do not have this problem with Outbound Rosetta Net integrations.