It's a bug that renders the challenge useless. Themis's workaround is useful if you use BL shelves for tracking books that you've read, but the book pages aren't accepting read dates from after 2019. Until the bug is fixed (if it ever is - there is no tech support here anymore), the challenge widget doesn't function.
That's probably at the very least part of it, but maybe not all. I just double checked by manually setting a reading end date to "1920/1/1". There are two columns in the bookshelf table, "date read" and "end reading". If the Y2K20 bug were the only source of the problem, both columns should now be showing the "1920/1/1" date, but actually only one of them is: "Date read". "End reading" is still blank -- so it's bound to be something else in addition to the date thing.
Still, if the Y2K20 bug is at least part of the reason, we can at least hope that it's affecting more than the BookLikes-specific servers ... and it may eventually be fixed; if not specifically for BookLikes's sake, at least for the sake of whoever else is affected by the bug.
http://themisathena.booklikes.com/post/2026074/work-around-for-date-read-end-reading-setting
https://www.tomshardware.com/news/y2k20-a-few-systems-arent-handling-the-new-year-very-well
Still, if the Y2K20 bug is at least part of the reason, we can at least hope that it's affecting more than the BookLikes-specific servers ... and it may eventually be fixed; if not specifically for BookLikes's sake, at least for the sake of whoever else is affected by the bug.