We have discovered a bug within the XML of the DDR Report that is exported from FileMaker Pro 15 Advanced (version 188.8.131.52).
On several of our files, the XML which is exported from the DDR Report will erroneously report that a "field object with a missing field ID" exists on a particular layout.
However, this is not true at all. There is no field object at all on that particular layout!
Even after deleting all the objects from the layout, even after adding a brand new layout part and deleting all the existing layout parts, even after recovering the file (with no problems found in the file), even after deleting all tables/relationships/fields from the entire file... the XML which is exported from the DDR Report STILL REPORTS that a "field object with a missing field ID" exists on a particular layout.
I would be happy to privately email you a copy of both the DDR XML report, along with a copy of the file as well... so hopefully you guys can fix this in a future update.