The first step is to look deeper into what may be happening.
Use Task Manager, Performance Monitor, and Resource Monitor to observe what all is happening on your computer while you watch YouTube Videos.
See if some application, process, or service takes all of the CPU, memory, drive read/writes, or network resources. For example some application may be trying to "phone home" and just will not stop doing so.
You did not mention any errors or warnings per se. However, Event Viewer may provide some informational log entry that corresponds with the pause times. May be many such entries as I read your post.
Start watching. Eliminate each possible culprit one by one until the pausing stops. Do so carefully so as not to shut down the system - find out, via some googling if necessary, what each application, process, or service may be. Disable and continue.
Just be methodical and keep notes - you may need to reverse some action on your part.
...if you're watching on a touchscreen device/display check it's clean
I had a similar issue with a game/app once, my character kept jumping when I wasn't even touching the screen, turned out it had a little bit of dirt across the play area lol
Cleaned it with a screen wipe then a soft , lint free, cloth