If you write a megilla, the mods often leave it for last, to make sure you didn’t slip in something inappropriate. If they approve it after a later post, the earlier post will appear after the later one that was approved first. That’s simply a function of how the software was programmed, and the mods have no control over (other than deciding which posts to approve first.)
Infrequently, a post may mistakenly get stuck in the spam queue until (and if) someone notices it and approves it.