If you haven't done so already, I would suggest you open a support case with the team at Support Case | Tableau Software . If you could include a limited log set with an estimated time as to when you tried to DL from the dashboard that isn't functioning and an estimated time as to when you were able to DL from one that works, it would help a lot.
My first suspicion is that the DL is simply trying to pull too much data. There may be work going on in the background that just isn't finishing before you navigate away. You could test this by trying the DL before you leave for the night and just see if it finishes.
I hope this helps,
Thank you for your reply. I did eventually identify a resolution to this, which was to lock the permission settings at the Project level, for the project where I published the dashboard.
Even though the users had the correct permissions assigned to them previously, for some reason they were not able to download data. Locking the permissions addressed this issue.
Gotcha. That would make sense too. Glad you were able to work it out.