As a current paid user, I find this embarrsing that the problem search feature does not work as expected. For instance, I tried "N-ary" and it didn't show up any single problems on N-ary Tree. Then I searched with "Tree", and it failed to show any problems with N-ary on the title, example: "Serialize and Deserialize N-ary Tree", "Encode N-ary Tree to Binary Tree" etc. This is obvioulsy wrong, as the Tree itself appears on each title.

This is not a corner case! It happened with other keywords I tried. Please fix these with a high priority, as this is very very useful and basic feature for any users!