I’m glad that you are pleased that I’m pleased that I was able to help!
When I first visited this thread, I saw your statement
A thread by new user Spora disappeared for some reason that I don’t understand.
accompanied by the relevant image, but I didn’t see your explanation of the sequence of events.
I deleted my own reply and the one awaiting approval, which was apparently an edit of the first post, and not a new one.
I believe it’s a standard feature of phpBB and other popular forum software that deletion of the first post in a thread results in deletion of the entire thread.