Nothing went wrong and nothing was lost. The search box and the filter panel on a Projects feed both do the same thing: they send you to the Projects search page, carrying your text and your filters with them. The feed you were on is not kept, because a feed cannot be filtered in place.
So a filter applied on Trending gives you a filtered search across every published project, not a filtered Trending.
Getting back to the feed
Use the Explore list in the sidebar. It holds Projects, All Projects, Trending, Award Winning and Atlas, and selecting one returns you to that feed with the filters dropped. On the search page, clearing the search box also returns you to Projects.
Which filters actually do anything on a feed
If you arrive at a feed with filters already in its address, or you remove one chip and stay put, the chips stay on screen whether or not the feed reads them.
- Trending reads none of them. It is built before any filter is looked at.
- Projects, All Projects and Award Winning read discipline and author.
- Country and organization never apply on any feed. Both are dropped before the request leaves your browser, so the chip sits above a list that ignores it.
- Date is unreliable outside the search page. Treat it as working only on search with the sort left on Relevance.
The search page is the only place where the whole panel is honoured, which is a large part of why applying a filter sends you there.
Search covers more than the feed you left
Projects search runs across every published, public project. Editorial picks, trending, and award winners are not separate collections there, so a project that was not on the feed you started from can appear in the results. That is expected, not a filter leaking.