Nick.

It means the post was removed either by the poster himself/herself within 5 minutes of sending, or a Pres/HL removed it.

There is no way for anyone here to determine who removes posts, but pretty sure Agora can see it, but they have never acknowledged when asked.

Next time you send a post, you'll see "edit/remove" and you have 5 minutes to do either. Run a test to see.