Lemmy.world has not yet upgraded to the new update that was pushed a couple of days ago because they are waiting on the captcha support coming in the next update (which should be soon). Once lemmy.world upgrades to the most recent version of lemmy (I think 2.8.1?), all the posts will sync again. Right now we are not syncing.
Sync issue for sure. In the support sub there's quite a thread about not seeing posts from other instances or not being able to post to them. It's pretty frustrating. Guess we have to wait.