Checkout option 2 of "how to find and subscribe to communities" in https://lemmy.blahaj.zone/post/61827. Basically, communities are lazily discovered only once a person tries to interact with the community. So you can teach your instance about a community by searching for it as described there.

There's maybe useful federation performance reasons why it works this way but admittedly the resulting usability is pretty terrible. Once you learn the required steps, it's not TOO bad. But figuring it out is bonkers. That post should get you sorted though.

I've found that I have to wait up to 30 seconds for a community to show up in the search. At first it says there are no results, but every community I've searched for has eventually appeared after waiting.

I think this happens if I'm the first user from my instance to use the community. The more popular communities show up straight away.

I've actually found the problem!

FIX:

While searching for community change sorting to 'New' and then it appears, any other sorting (Top All Time, Top Day, Old, etc.) just doesn't show some new communities.

I've had the same issue with subscribing to Computer Science on the .ml server. I'm not sure why.

I’m having the same problem with a community I started, https://lemmy.world/c/avtech

Lemmy.world can see it fine, but I can’t seem to hit it through other instances.

Tried on Beehaw and Lemmy.ml, tried by searching using !avtech@lemmy.world and the URL, either way is no result. I can find my !newcommunities@lemmy.world post just fine, and tried follow the link but getting 404s there too.

I have the same problem. I can't find some communities when 'All' is selected.

Seems to me that is communities creator fault. Maybe they didn't do federation to other instances.

I used this to search for lemmy communities https://browse.feddit.de/

I just followed lemmy.world without creating an account here from lemmy.ml