It happened again, when posting the other post (about newsbin.nbi.bak).
Knowing that I copy my text to a clipboard manager first before hitting the preview button.
Was using Edge, but it also happened whilst using Chrome.
I drafted the same post 3 times and could post it the 4th time only.
Maybe it has something to do with some sort of inactivity counter?
(btw: whilst drafting this post I was logged out as well ...)
Meanwhile, the notification mails still mentions forums.newsbin instead of forums2 newbin.
Could that be changed?