In the new (preview) web interface, the warning triangle shows up on a dataset with the hover-text "...Select the warning icon to view details". However, clicking the icon does nothing. You actually have to click on the "schedule refresh" button and then click on refresh history to see the details of the refresh failure.
Suggestion: Add a link in the icon (as suggested by hovertext) or change the hover-text to have the correct instructions.
Thanks,
Aaron