What would that have been about ?
You have three posts in your other topic
https://forum.avast.com/index.php?topic=200168.0 and one in this topic..
There is a bug in the forums software that on occasion eats the post, some copy before posting, some use preview (so it doesn't time out) and that greatly reduces the chances of having a post eaten.
It that did happen your text input screen would be blank, using the browsers page back this often restores the data, preview and then post.
