BPA lines not showing when searching the iProc main store

We have two iProc responsibilities - one for users who order items from Inventory, and one for users who order the same items from the external Suppliers to replenish Inventory stock.

Some lines on a BPA are not showing in the iProc main store, but other lines are.  The only difference is that these lines have a different purchasing category to the other lines.  I have checked all of the set up for these categories and it is the same as those categories that are showing in the main store.  When searching using the item number or description, no search results are found.  This is when using the responsibility that should see the external supplier items.  Other lines on the BPA show when searching for them in the same way.