Here, @drorsun has explained the issue: https://github.com/akiran/react-slick/issues/300
and here is the sandbox to play with: https://codesandbox.io/s/slick-slider-react-slick-bug-with-video-forked-967b5?file=/src/index.js
So what's happening here is, we are trying to implement autoplay video on center mode, and since the react slick has cloned the divs multiple videos are playing so only the video on top can be played or paused with controls but there is a video still playing the background.