I just joined the NZ lemmy here, because Lemmy.world was slow.
This instance is much faster for me, but when searching for communities, many that I was subscribed to with my lemmyworld account didn't show in the search results.
I fixed this by manually finding it in the address bar, like this:
https://lemmy.nz/c/[email protected]
And this will work for all communities, just replacing the appropriate parts:
https://lemmy.nz/c/[communityname]@[instancename]
Then you can subscribe and it will show in your 'Subscribed to communities' on the main page. (sometimes I have to refresh for all to show up).
This might be a known issue at the moment, but I've only been on Lemmy for like 3 days so idk