Looking forward to a solution for this issue. We had to disable Endpoint probe on the isepic so we would not get "not found" users in the FMC that the isepic was subscribed to. Basically, user to ip mappings were sent from isepic to FMC, and for whatever reason, the culprit of those failures to insert into that data into the FMC database, was the endpoint probe running on the isepic.