Hello Kuba,
Ok that is very strange. I am going to guess your theme is doing something very weird or the component output has been disabled on that page since we load fully in php/html not JS so that shouldn't be an issue.
Can you try with the default protostar template firstly.
IF that works you need to review how your theme is set for that page?
Also check for html/com_jevents in your themes root.
Many thanks
Tony