Categories don't display posts

Hi,
I installed newest version and posts don’t display when I click on the category:
https://mieszkaniewpigulce.pl/index.php/category/category-1/
even whenI click on the default one:
https://mieszkaniewpigulce.pl/index.php/category/uncategorized/
post are properly assigned to categories:
https://mieszkaniewpigulce.pl/index.php/2015/10/20/this-is-my-third-post/

I don’t know what I did wrong.
I made default installation, without any customization. All other options (links) work properly: Recent Posts, Archives, work correctly.
I tried to install older version 4.2 but had the same problem.

Thanks for your help,
Piotr