I was trying to filter my to-read pile by books added to my reading challenges and it stayed on filtering for a while and then returned no books. I've definitely got lots of books added to reading challenges.

I was originally trying to filter with both that check and some tags, but also made it so that the reading challenges check was the only filter. Both said "filtering" for probably 10-20 seconds and then returned no books. I'm on Firefox if that makes any difference. (Sorry, not sure how to help replicate this one.)