Currently there is a bug where new posts show up at the top of the feed when browsing under any sorting method. According to this github issue its been fixed in a recent release. Could lemmy.world be upgraded to this version?
EDIT: Looks like the release is not out, had thought I saw a release tag for 0.18 but it was the RC. Hopefully its out soon :)
There was an attempt to patch the server to the first release candidate two days ago. It didn’t went well: 500 error appeared, and the patch was reverted. You may see the details here: https://lemmy.world/post/226641