File Adapter messages stuck in “To Be Delivered” status

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Symptom
You have upgraded to PI 7.0 SP 18 and you notice that File Adapter messages are stuck in “TBDL”(To Be Delivered) status. Additionally, the following symptoms are noticed:
1 – File Adapter stops polling
2 – NullPointer Exceptions are seen in Audit logs
3 – Hanging file adapter locks are visible in the ‘Locking Adapter’ [...]