How can I correctly show these two fields? (They have suddenly stopped working)


Just to be clear, the image you shared was of a WTPart and you highlighted the "Described By Documents" and "Reference Documents" tables. These tables would show related Documents.
Scrolling further down (cut off in the image you shared) is the "CAD/Dynamic Documents" table which would show related CAD Documents.
In Windchill, Documents and CAD Documents are two different things!
You showed another image where you were trying to search for the CAD Document, but that search window looks like it is for Reference Documents. That won't return CAD Documents, only Documents.
Links in Windchill are bidirectional, so if you see the link you're looking for on one object, it is for sure on the other object. You may just be looking in the wrong table. If you are looking in the right table, make sure that the table isn't filtered and that the View you're using in that table isn't omitting the items you're expecting to see.

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