The list seems to work as expected. If there are no questions with a bounty, the "featured" tab is hidden.
This happens even on the normal bounty page, as well. To see this, you can go here and see something similar to your error.
I think that the site remembers your favourite/last used tab. That tab, in your case, must have been the "featured" tab, which then disappeared once the bounties expired.
To replicate:
https://skeptics.stackexchange.com/questions/tagged/nutrition?sort=featured
To "solve", just choose a different sort, e.g.:
https://skeptics.stackexchange.com/questions/tagged/nutrition?sort=newest