EMM cause (LTE NAS)3GPP TS 24.301 §9.9.3.9 and Annex A
What it means
Illegal ME: the device (not the SIM) is blacklisted, e.g. by the EIR.
Where you see it
In LTE NAS Attach reject, Tracking area update reject, Service reject or Detach request.
What to check
Check the IMEI status in the EIR.
Look at the S6a (MME↔HSS) and S11 messages just before the reject: they usually show the real trigger.
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