In the Work Order module for one of our companies, we have the settings set to:

Work Order Issue Method:  Backflush
Auto Generate Material Transactions:  Yes
Auto Generate Labor Transactions:  Yes

This has been working, but every now and then we get this message upon entering a completion transaction:

And sure enough in the auto-generated Material Transaction, nothing is auto allocated.  I can go in and Manually Allocate, which I did for this case. 

But I wanted to find out the "why" so we could avoid it for next time.  Any thoughts will be appreciated.  I can provide more background info if needed.

Sage 100c Advanced 2018 v6.00.10.0