Thanks for your reply, but unfortunately it's not working like that. What i described above was happening after creating about 40 notes, several hours and they all looked pretty, then they were either not existing anymore or in a not-edited version.
It happenened again yesterday and today, even though I'm now super disciplined, I close the note with the "finished" button (my version is German, so I don't know if that's the label), I even reload the page after each note, then fine, everything is still there, open the app on my mobile, and bam ... everything changed again.
Today it changed the note while it was open and I was working on it!
I'd really like to use Evernote since there are so many good recensions about it, but it just not working ... ?