Weird, that fixed it. I assumed that since the URL was exactly the same whether I ran it with ./nodebb start or ./nodebb dev, it couldn't be related to cache. I suppose I just don't know enough about how caches work.
Thanks anyways π
Check this change out: https://github.com/designcreateplay/nodebb-theme-vanilla/commit/cc7317090cc8a8582390db97cc7b742d5275fe82#diff-b2d5dbbac0a14c90415afe088651032a
If you have a customized category.tpl you might want to merge these changes in (otherwise, upgrade vanilla / core)