Did happened to me in the past by mistaken clicking on add topic after entering text.
Knowing that Chrome saved the text in cache I played with page forward or back and the text appeared.
Learning from that, I write in Word and then paste - If I loose it I paste again...
My suggestion for the developers is:
1. When text is entered to treat the "add topic" the same as "save" or
2. Gary out the "add topic"

That will eliminate confusion for the casual user.
As can be seen in the attached screen print, depends on the window size, users will not see the "Save" and naturally will click on "Add topic"

Thank you 

Thank you, yossik! I managed to restore it from a DB copy!

But, Robert, I noticed that the italic doesn't work at all in our wpForo. For example, see the "test italic" comment:
https://glue42.com/community/questions/how-to-manually-run-zaps-integrations-at-zapier-com-for-real-time-results/#post-47

Our Custom CSS Code contains only this:
#wpforo #wpforo-wrap {
   font-size: 13px; width: 100%; padding:10px 20px; margin:0px;
}
  #wpf-widget-online-users .wpforo-widget-content a.onlineavatar{max-width: 64px;}

Any idea how to fix that?

@Robert, you're correct.

Click again on add topic does reveal the text, but...
Go and explain it to the end users.

But, Robert, I noticed that the italic doesn't work at all in our wpForo. For example, see the "test italic" comment:

Use this CSS code:

#wpforo #wpforo-wrap .wpforo-post-content em {
    font-style: italic;
}

Thank you, Robert. I added it to the Custom CSS Code. However, it still shows the italic texts as regular texts.