STEPS
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The issue can be reproduced at will with the following steps:

1-Run the Min-Max Planning report with option Restock for Item X which is under Min

2-Run the the Requisition import with the option "Initiate Approval after Reqimport" = No

3-One requisition is created in Incomplete Status (and the destination type is Inventory and destination subinventory exists when checking in PO_REQUISITION_LINES_ALL)

4-Open the requisition in iProcurement

5-The destination type is changed to "Expense" and the destination sub inventory disappears from the table PO_REQUISITION_LINES_ALL

Solution

Set the profile option 'POR: Preference - Selected Items Default to Inventory' is set to 'Y' for the user who opens the requisition in procurement