I have a modern computer with a fast processor. Wonder why the sound cuts in/out on playback. see http://wildirisconsulting.com/dorico/IMG_3144.MOV
I have the same problem from time to time. I also have a fast computer and processor, but a crappy built-in audio engine. You might be in the same boat.
Try increasing your buffer.
If you’re running Mac the issue may be related to this known problem: Is Apple's T2 Chip Ruining Producers' Recordings? : Ask.Audio