Why does K2 in Joomla 3 display an empty block instead of content when I added an owl-carousel to it and an item to each material?

Question

JavaScript

K2 displayed normal material, but I needed to make a slider out of it.
I tried to initialize owl carousel 2 in K2 template. Added an owl-carousel class and added an owl-item to each item, then all the content was gone. no owl no item, nothing else. Why could this happen? and how to treat it?