Steps to reproduce:

1. Use the "Search Everything" input to search for something with special characters. Example "Freedom of Movement" (including the quoatation marks)
2. Search result page is displayed as normal
3. Click on the "Character" filter
4. Search result page shows 0 results
5. Check Browser URL. It should show something like this: https://www.dndbeyond.com/search?q="detect thoughts"&f=backgrounds,classes,feats,races,spells&c=characters,spells
   1. Note the html encoding of the quotation marks "
6. Change the " in the URL into normal quotation marks and hit enter
7. Search result page shows several results again (filtered for the category you chose in step 3)

I think I had this same problem when I searched for something with an apostrophe, then selected the "Characters" filter. The apostrophe and everything after it get erased.