I have a 2017 MacBook Pro running High Sierra 10.13.6.
I have noticed some phantom behavior and am curious if anyone knows what is causing it. It usually occurs when I am typing, either an email, some text or some code. Suddenly I can no longer type (as if my Mac has changed to another program) and all the icons on my Dock sort of vibrate and jiggle around. After a few seconds this stops and I can click on the program I was using and I can continue. If I try to continue my program while it is doing its phantom thing, it just goes back go the phantom behavior. It looks as if it reverts to the Finder instead of the program I was using.
I plan on upgrading the OS soon anyway, but was curious if anyone else has noticed this. It happens at least once a day.