2700198 - Cannot edit a purchase requisition in Fiori apps - SAP S/4HANA

When trying to edit a purchase requisition in the "My Purchase Requisitions", "Manage Purchase Requisitions" or "Manage Purchase Requisitions Professional" app, the system returns one of the following errors:

• Purchase requisition & does not contain any changeable items (06 800).
• You cannot edit or delete PR (MM_PUR_REQN 018)
• Purchase Requisition is complete. Further editing is not possible.

However, the same PR can be changed in transaction ME52N.

• Materials Management
• SAP Fiori
• SAP S/4HANA (All versions)
• SAP S/4HANA Private Cloud

FIORI, F2229, PR, PREQ, REQ, F1048, MM_PPR_MAINTS1, MM_PUR_PR_PROFNL_MAINTAIN_SRV, MM_PR_PRCS1, MM_PUR_PR_PROCESS_SRV, PROFESSIONAL, 06 800, 06800, Contract, PO, Purchase Order, Manage Purchase Requisition Professional, MM_PUR_REQN018 , KBA , MM-FIO-PUR-REQ-SOC , Fiori UI for Sourcing Purchase Requisitions , MM-FIO-PUR-REQ-PRF , Manage Purchase Requisitions – Professional , Problem