I've had several posts disappear like that since the revamping of Mudcat. Sometimes there's an obvious explanation, e.g., a delay in transmission or something. But in some cases, the "submit message" process seemed to go without glitch, yet the post isn't there the next day. I can't swear to this, but I think I've even had a couple of posts disappear after I've opened the thread and seen them there.
And I doubt that any of the ones I'm referring to would have been censored.