Using MNC 999 MCC 999 or 99 for Private Enterprise Networks

Hello, I am currently in the process of testing our 4G Private Enterprise solution with all tests successful apart from any iPhone/iPad tests. It appears that the use of MNC = 999 MCC = 999 or 99 the IoS devices would not attach to the network, however once we changed to one of our clients reserved MNC MCC values the devices start to work normally. Could someone confirm this to be a known issue and is there a planned fix. Thanks Kevin