"Hi, I'm a new user. Where did my posts go?" the explanation.

New / low post users are placed in a special user group.

Suspicious "spammy" behaviour triggers filters.

Some of the reasons without giving away the filtering at work:

Posting urls
Posting email addresses
Trying to sell stuff
Linking to ebay
Etc.

You're a new user! Introduce yourself in the introduction forum.
Read a bit, post a bit.

If your first post is 400 words long with 25 urls IT WILL trigger the filter.

People flagged as suspicious have ALL their posts placed in moderation until they
can be verified. This can be retroactive, aka "where did my posts go?"

Moderation can take between 12hour-3days. It requires human viewing and
intervention and thus takes time.