Thanks for your reply!
So I checked file permissions and they are 755 for wp-admin, wp-content and wp-includes as well as for all subfolders.. I checked changing it to 775 but that didn’t help…
Another interesting thing I found is that I am actually getting my page displayed incorrectly because my browser is blocking mixed content from my page. If I unblock the elements the page shows correctly. And the elements are CSS files from the folder ../wp-content/uploads/themeisle-gutenberg/.
Does that give you any new information on what the problem could be?