Error: The material sourcing process failed to create picking suggestions for line 1 of move order n

Release 12.1.3

Problem encountered during pick and ship process for simple sales order.

Raise sales order and book.

Perform pick release for specific sales order. Pick slip has No Data Found message, even though stock available.

However, go to Transactions form and following form is displayed:

Navigate to Transact Move Order:

Now I appreciate that this is probably due to reservation failure of some sort, but there is plenty of stock, and availability checks show no other reservations.

I've been through numerous documents related to this, but drawn a blank, and really stuck now for any new ideas.

Auto Allocate and Auto Pick Confirm both set to NO.