It's unclear from your question whether "all data items" are missing (as the subject line says), or only "a few data items" are missing.
If that's the first, you may have messed up with Subject_ID_1 (Subject_ID_2 etc) custom properties that control folders and data items visibility by subject levels. Double check those, referring to SAS MA Administration Guide that explains custom properties usage.
In only a few are missing, then what differs those that you see vs those that are missing? If you used Level = ID then such data items are supposed to be missing. Don't use Level = ID if you need that data item available for selection, use Nominal, Nometadata instead.
Good luck!
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Dmitriy Alergant, Tier One Analytics