Lastly I saw a message on the page history of the Main/WebHome page. This message is a line in the history with a link to a more current version.

"Version coming from extension XWiki Standard Common Application 15.7"

This message is put in a data cell with a colspan of 4. This makes the table look all crooked (see image). After I changed the colspan to 3 the table was nice and straight again.

Thanks for all the work