Hi John,
Thank you for the feedback. That is strange that you're no longer getting prompted....let me know if this issue happens again and we can proceed from there.
Out of curiosity though, at what point during the download were you getting prompted? i.e. in the screen where you picked the extent and level of detail or only after you had clicked 'Download Area'?
To answer your question, yes that does sound similar to my testing scenarios. I used an instance of ArcGIS Server > secured with token authentication > I then added this service as an item into My Content in AGOL and stored those credentials. Again, the problem we were seeing originally happen during sync, you would get prompted to enter in credentials.
Thank you for the feedback. Let me know if that happens again.
-Kevin