Could be any number of things, P.H. I know that I have deleted a couple.
Chatter on threads that is unrelated to the script itself (“Is Celtix any good?") will frequently get deleted. That is what PMs are for.
Even worse are reviews that are unrelated to the script itself. One sentence reviews -- or short comments where the grammar is intolerably poor -- or where it appears as if the reviewer has not even read the script -- those go, too.
Those are deleted on sight, lest new members think such behavior is the norm, and then mimic such behavior.
I will also delete posts where the poster helpfully dispenses formatting advice that is patently incorrect.
People who start too many WIP threads for multiple projects (ahem) will sometimes find those deleted, too -- though we have been a bit lax about that lately.
If you have had a post disappear, maybe check the
rules and see if you can figure out why.