Some posts and comments doesn't sync to other instances.

I noticed that some of my posts and comments in the community I created (!skypictures@lemmy.ml) doesn't seem to sync to other instances.

For example, if you go to the community through lemmy.ml and lemmy.world you won't find the welcome post through lemmy.world. But the post I put just after that one do appear. The same issue also seem to occur with the sidebar.

Can anyone help fixing it?