Horizontal Line Won't Appear!

I am using the Oxygen Theme. Usually, I can create a horizontal line between paragraph in a post. But lately, I don’t know why, each time I add a horizontal line to my post, it will only appear on editing page, but nothing on the real site. I checked the HTML of the post, and there were many codes like <hr /> but still no horizontal line on the real site.

What should I do? Can anyone please help me?

https://aetasiter.wordpress.com/2016/07/26/sekilas-tentang-itb/
^ on this site, there should be a horizontal line each after a paragraph, but nothing there

thank you in advance!