However it looks like that middle term is actually irrelevant, meaning; /contests/[cat-slug]/[item-slug] is the same as /contests/[item-slug].
If I’m right in guessing that ( and [cat-slug] is just decoration ), then you might have two options;
WILDCARD REDIRECT
/contests/(.*)/(.*) → /contests/%2
If this works, you’d be able to use your URLs, but they’d redirect to the Webflow standard version.
REVERSE PROXY
Building a reverse proxy would allow you to keep that URL in the path, and in this case you don’t need a path translation map, you can just ignore the middle term.
I build these if you should need some custom dev work done.