I have the same problem. I canโt find some communities when โAllโ is selected.
Seems to me that is communities creator fault. Maybe they didnโt do federation to other instances.
Problem with that is that there are lots of new instances, hard to keep on top of that all the time.
Thereโs a useful community called New Communities (or similar) - Iโll add a link here shortly.
EDIT - https://lemmy.world/c/newcommunities
Also, very useful is https://browse.feddit.de, which lets you search for communities across all instances.
@splitcircus @JustineSmithies can federation be disabled when creating a community? is it enabled by default?