The responding GTP-C node itself is congested (GTP-C Entity Congestion) -- a capacity/load issue on that node, not a policy rejection.
Where you see it
In the Cause IE of a GTPv2-C response (Create Session, Modify Bearer, Delete Session…) on S11, S5 or S8.
What to check
Check with the remote operator whether that node was overloaded at the time of the attempt.
Check which node sent the response (MME, SGW or PGW): the cause belongs to that node's decision.
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