As
@Eighty said, those first post threads by new members have to be approved by a mod before they post. Something in Xenforo must be tripping the new thread notifications prior to approval. They're deleted for reasons already covered (spam).
This.
I'm usually on checking for spam until midnight MDT or later, often until 0200 and sometimes later.
Very few are getting through since the new settings were deployed. Same thing I'm seeing over at HDRams.
There's some TLD restrictions also in place, and (I believe) a secondary spam honeypot.