I see this has not been answered. I do not know the answer, but maybe a short explanation of possible reasons would be helpful to you and others. 1.
Might have happened accidentally. The site sometimes experiences problems. Mods also might be attempting to delete spam or off topic posts and make a mistake. 2.
Duplicate posts get deleted. Was your post your own OC or one made by someone else? Off-topic posts for this thread would also be deleted. 3.
If the OC involved one of the images we removed at Chloë's request, then it gets deleted without comment - if there was a big discussion it would draw attention to the very pics that we're hoping will become LESS publicized.
4. Fakes and disrespectful pics get removed, but there is a warning and/or a ban. So, that was not the case for your post.
So, if you repost in the numbered thread, it is likely that a definitive answer can be provided.