hi,
After booting the MS should send a location update, and go through all the security steps to attach to the network.
It would be best to do a trace of those messages (either from MS itself, or from network probes) to understand why the NW is rejecting those MS. You’ll see a reject message with a specific cause of rejection.
Do you have access to such probes ? In E/// you can trace directly from GPEH or CTR.
regards
pix