All right, I've got more informations about this one.
First I checked different browsers - same problem.
http://i.imgur.com/Z1u8Twu.png
Then I cheked other devices (phones with LTE connection/tablets/PCs in school) - same problem.
After that I checked this situation in Tor Browser - for some reason it works propetly.
http://i.imgur.com/mQ6KUVc.png
I think that there might be something with connections to Polish IPs.