I think spotted an example of federation failing between lemmy.ml, even after the update to 19.2, and Lemmy.world, which is still on 18.5.
If you look at the TenForward community on lemmy.ml (https://lemmy.ml/c/tenforward@lemmy.world?dataType=Post&sort=New) and compare to its lemmy.world version (which is its home) (https://lemmy.world/c/tenforward) … you’ll see lemmy.ml is behind about 2 days.
Haven’t seen any other examples like this, even from lemmy.world though I haven’t gone looking for them either.
If the community does not have a follower, new activities may not be sent. For example, you can check !videos@lemmy.world which is more mainstream community, they’re federated.
https://lemmy.world/c/videos?dataType=Post&page=1&sort=New
https://lemmy.ml/c/videos@lemmy.world?dataType=Post&sort=New