Twenty Fifteen: IE 11 not displaying header image

Hi,

I am developping a website with the twenty Fifteen theme. In Internet Explorer the header image doesn’t appear most of the time. Sometimes it does, sometimes it does not, sometimes refresh solves the problem, sometimes not???

In all other browsers this problem does not exist.

Here is a link to the site:

https://www.th15669-web521.server52.vorschauseite.eu/801_demo_dolders

Thanks a lot for your help!