Displaying products of subcategories looses all styles

Hi @all,
I'm running an OC 2.2.0.0 with "thekitchen" theme.
I've only 1 category where subcategories are available. All other categories have their products right under them.
All products within a maincategory are displayed correctly, but when I try to show products of a subcategory all stylesheets seems to be lost.

You can make you are picture of the behaviour when you open my shop at: https://www.dankebauer.com

In the top menu you can open "Produkte" (which stands for products) to display all the main categories. If you choose the first one "Aufstriche & Butter" (which stands for "spreads and butter") you see the correct display of the products list page.
But if you choose the second item "Brot (Bauernbrot)" (which stands for "bread") you see the 2 subcategories. When you now choose either of this subcategories you'll see the crashed product list of the choosen category.
With the firefox dev-console i found out that many .js files could not be loaded. Due to the fact the the url is simply wrong. Firefox states for example, that the desired url https://www.dankebauer.com/brot/catalog ... tom.min.js could not be loaded. But when i examine the url and extract the maincategory name "brot" from it, the file can be loaded. So the working url will be: https://www.dankebauer.com/catalog/view ... tom.min.js

But I've no clue, why the system is generating urls with the category-name to load .js files.
Any ideas from you, how I can fix that?
The solutions to put all products under the main category is not suitable

Every hint to solve this problem will be appreceated.
With kind regards.
René

I found out, that the display works well, when i delete the SEO tag for the category.
But in my opinion this should not affect the display, only the url in the browser for better reading.

Any Infos regarding this?
Thanks in advance.
René

Du bastelst jetzt schon seit dem 15. Juli 2016 an diversen Problemen.
Sehe sehr viele Baustellen an diesem Shop - warum nimmst dir nicht mal einen vernünftigen Entwickler?

Hallo OSWorX,
wie es scheint, habe soeben Deine Website besucht, scheinst Du so ein Experte zu sein?
Übernimmst Du also auch Auftragsarbeiten wie zb. Update des Shops inklusive den schon installierten Payment-Modulen, in dem Fall mPay24 usw?

Oder Anpassungen die DSGVO betreffend?
Wir betreuen nämlich nur diesen OpenCart Shop und haben daher nicht so eine umfangreiche Erfahrung, als wenn es unser tägliches Business wäre.

Vielen Dank im Voraus
René