Probably because you made two posts that were practically the same topic?

You made 2 threads on the same thing thus one of those threads got removed.

As per the FUG:

Posts will be removed and the user may be banned (either temporarily or permanently) if:
the post is one of multiple copies in different forums;

sud0:

 

Hi. Why am I getting 404 when trying to access a post that I made in a forum today?

 

I have restored it, while changing the topic subject and message on that thread to make it substantially different from the other one you created about the same time.