According to This you are . Perhaps they haven't been pulled in yet. Try subscribing to a sub there and it should start syncing posts (as I understand it).
how are you searching for them? i find it's typically best to search via url, so if you're looking for their Homebrewing community, you'd put https://lemmy.radio/c/homebrew in the search box.
it's a little strange in that if it's a new community to this instance (never searched or subscribed to before), it will initially say "No results found", then a few seconds later will bring up the result.