I know that Morris has mentioned that he occasionally loses his post.
It has happened to me a few times too, and I;ve put it down to clumsiness - hit something 'wrong' instead of the 'submit' button.
But tonight I think I've spotted it -
Using Quick Reply, when I hit Submit, my post disappeared, but I then noticed that in the meantime someone has posted a new reply that wasn't there when I started! That's what flashed up when I thought I should have seen my post.
Fortunately, if I'm doing something wordy (and important LOL) on both here and other places, I prepare my words first in Word, then copy and paste in here, and can hit Submit immediately without getting confused and losing work.