CSS not rendering in loop at 1st visit (only after ajax fetching)

Hi,

I’ve been working a long time on my theme and after opening my browser lately I found out that my CSS is not working properly in the loop. Everything else (Header, Sidebar, Footer) just works like a charm and is rendering correctly.
Funny thing: If you click on “Mehr Artikel laden” (Load more articles) at the bottom of the page, the whole stylesheet will display as it should. As well as if you close the site and open it again (just not by first visiting after opening your browser). How’s this possible?! Look at this link. (Sorry for the shortening, I don’t wanna have my page indexed)

Also, I made an extra template for a special category. The CSS is working in this loop (look here), BUT it’s causing me problems to fetch new posts (try the load more-button..). The common paged-navigation with two links is working, which is really strange (but I want the dynamical loading.. :D).
I tested my category-template on the index-loop and the CSS will work, but of course not the navigation.

I can’t tell the problem, have tried so many things and ended up here because I couldn’t find a solution..

Best,
2trees