3261273 - Unable to view subcontracting components

You have created a purchase order with item category 'L' for sub contracting. 
In the change purchase order - advanced APP, when you navigate to the Item >
Material Data, you can access the sub contracting components via the 'Bill of Material' Icon.
There are some cases where the icon is missing and you cannot check or change the components.  

SAP S/4Hana Cloud - All versions 

1) Create a Subcontracting Purchase Order via Create Purchase Order - Advanced (ME21n) 
2) Open the PO Display Purchase Order - Advanced (ME23n)
3) Go to the Material Data TAB 
4) The Bill of material icon is missing from the screen 

Multiple Schedule lines. 
If the delivery dates are spread across more than one schedule line then the screen field in the material data TAB is suppressed.
 
 

The components are maintained per schedule line in this case, so you find the access to the components under the Delivery Schedule TAB.

LMEPOF8D, lclfs_mmmfd_bom, LCL_1319_VIEW_MM, LMEGUICI5, mmmfd_bom, metafield 236, MM06EFLB_MDPM_MAINTAIN, ME_COMPONENTS_MAINTAIN , KBA , MM-PUR-GF-SCR , Subcontracting in Purchasing (Repair) , Problem