Why don't I see the same posts when browsing a community from 2 different instances?

If I open: https://lemmy.world/c/lemmy_support@lemmy.ml and https://lemmy.ml/c/lemmy_support in 2 different tabs, I don't see the same posts at all, even with the same sorting option selected.

Is it just because the servers are overloaded and there is some delay in the synchronization?