Used to be I'd click Add a Card at the bottom of the List, type # and the first few letters of the label, and it'd filter me the appropriate options. Super convenient as I wouldn't have to bother with the awkward labels UX.
As of today, that seems to not be working, even though it was working 2-3 days ago.
Tested in incognito mode and same thing, so it doesn't look like its happening locally..