Hi,
It does not happen anymore. I guess it had to do with a code i used for a plugin to show articles. I made a shortcode for the code and after that it doesnt happen anymore.
I had the problem in multiple browsers and cleared cache etc.
The only problem what happens now is that the shortcode disappaer. After editing the page. When i save with shortcode it works. When i edit it for the second time the shortcode disappaer. I added it in a paragraph box.