Are you processing MFBF in background if yes you can have a problem in the BOM components.
Check if the BOM assignment is correct
Check if on MRP view and check if the components have assigned the production storage location.
Once you ensure the BOM and COM components are correct try to process foreground with the option "Post with correction" you will be able to see if any error on the component is causing the issue.
Hopefully that can help.
Regards,