Has this app design worked for you in older versions? I tried something similar before, and it has never worked for me, even in the older versions.
As I understand it, the Drop Down Tool loads its data as part of loading/opening the app, so it happens before your user can upload their file to the File Browse Tool.
If I really need to take the data from the user's file, I'd use Chained Apps. The first app uses the File Browse Tool to take the file from the user, and then create/update a file/database in the backend. Then, the second app has the Drop Down Tool that references that file/database.
