Line Type LOV is empty when entering New Requisition Line in RSSP

Summary:

I am having trouble with RSSP for one client where the Line Type field is completely blank when we use Enter Requisition Line. No values are being returned in the LOV.

If we create a Non Catalog Request or use a Smart Form the Line Type is fine - the issue is only with using the Enter Requisition Line function.

We had the same problem when enabling it in a lower environment, and then after weeks it miraculously resolved itself. However we have now enabled it in a new environment and the issue has occurred once more.

I have run all the recommended ESS processes and so I don't believe it should be anything to do with that.