When you try to open a link pointing to a tag that mostly leads to adult contents, or a blog flagged as adult, then you may receive no search.
Even though the app is now rated 17+, content from NSFW or adult blogs won't show up in searches. Moreover, many specific tags no longer.
Tumblr's adult content ban is already harming the site's vibrant community. searching for the NSFW tag no longer generates any content.