EMM cause (LTE NAS)3GPP TS 24.301 §9.9.3.9 and Annex A
What it means
Severe network failure: the network has a lasting problem and the phone should not retry for a while.
Where you see it
In LTE NAS Attach reject, Tracking area update reject, Service reject or Detach request.
What to check
Check the core network (MME/HSS/SGW) for a major outage at that time.
Look at the S6a (MME↔HSS) and S11 messages just before the reject: they usually show the real trigger.
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