Begin by addressing some coding errors. It’s likely that these will mess with layout.
1. In your header.php file, Remove the gap between < and ? for your content-type meta tag:
<meta http-equiv="Content-Type" content="text/html; charset=< ?php bloginfo('charset'); ?>" />
becomes
<meta http-equiv="Content-Type" content="text/html; charset=<?php bloginfo('charset'); ?>" />
2. Get rid of all link closing tags. The link tag is self-closing and does not require a separate tag for closure.
E.g.
<link rel="alternate" type="application/rss+xml" title="RSS 2.0" href="https://www.hobbieblog.nl/cms/?feed=rss2" />
</link>
becomes
<link rel="alternate" type="application/rss+xml" title="RSS 2.0" href="https://www.hobbieblog.nl/cms/?feed=rss2" />
3. Remove the </meta> tag. Again, meta tags are self-closing.
See if the above fixes your issue?
J