I am having a problem with YouTube videos being both choppy (even at the lower resolution) and the sound not matching the people talking.
Although I have older machines and use the 32 bit flavor of Kubuntu, I am surprised that the apps are sloppy with this OS. I have used all of the
Ubuntu flavors for over 5 years and that is my biggest disappointment with all of them. I have four machines with Ubuntu and one on Windows
(for gaming purposes) and cruise the internet extensively. I'm very used to Linex as well, as I worked as a trainer for a major firm that sells Linux
software to the automobile business. Typically the refresh rate is more than adequate. Any suggestions. Oh, it has nothing to do with internet
connections and through rate. This household sees a whole lot of internet useage.

This could just be a problem with the browser, especially Chrome tends to misbehave when too many tabs are open, as it tends to use too much memory
You didn't tell which browser you use for playing ...

I very much doubt this has anything to do with Linux or Kubuntu.

I am having the same issues with firefox. I'm using the latest plasma that has come through manjaro. I'm gonna try changing the video driver. Using rx 560 video card. For me YouTube videos are choppy for 10 seconds, and the words don't match up.