Symptom:
UE sends multiple Service Request for mobile data but MME never responds until UE gives up and try with Initial UE Attach.

Conditions:
In 3G->4G TAU, after MME sends TAU Accept (with new GUTI), UE sends another TAU Request (with newly assigned GUTI) and then sends TAU Complete. After receiving TAU Complete, MME sends TAU Reject so the MME never maps the newly assigned GUTI with the UE. Later UE sends Service Request for mobile data but MME never responds to it