Steps to replicate the issue (include links if applicable):
What happens?:
You end up at https://incubator.wikimedia.org/wiki/Wy/cs/Wikivoyage:Hlavn%C3%AD_strana
What should have happened instead?:
You should have gotten to https://incubator.wikimedia.org/wiki/Wy/cs/Brno
I think in the past this did work correctly.
Permalink to a user's report: https://incubator.wikimedia.org/w/index.php?oldid=6202463#URL_redirection_broken_in_interwiki_links