mod_pagespeed css shown render blocking?

Question

I've already found this topic concerning my problem and figured out Google is about to discuss a fix of the blocking js. However, could somebody please check out my client's site squarecard.de with Google Pagespeed and explain what else is going wrong there?

For some reason, I get:

1. Slow Server Response (TTFB issue with Wordpress?) - Any easy way to bring it down to something like 0.3s? (Look at zaunschilder.de, which is hosted on the same vServer, TTFB performs great there)

2. mod_pagespeed CSS blocking render and obviously not being combined. My mod_pagespeed config is:

   ModPagespeedEnableFilters rewrite_javascript,rewrite_css
   ModPagespeedEnableFilters elide_attributes
   ModPagespeedEnableFilters prioritize_critical_css
   ModPagespeedEnableFilters defer_javascript
   ModPagespeedEnableFilters sprite_image
   ModPagespeedEnableFilters convert_png_to_jpeg,convert_jpeg_to_webp
   ModPagespeedEnableFilters collapse_whitespace,remove_comments
   

Ideas, anybody?