So this has been making me crazy for awhile, and I haven’t come across a solution for it online yet… Every now and again, I’ll accidentally swipe up with three fingers on my 2015 MBP running High Sierra, and Expose will animate half way through and stop. Then I have no keyboard or touchpad, and my only recourse is to hard boot the system, which really sucks!
UPDATE: Further testing shows that when the the display changes, keyboard commands do not function until the transition is completed. Using three fingers, you can slide up or down on the trackpad to complete the transition from one app window to many and back. When the transition is completed, the keyboard responds. I tend to see this on web pages that have a lot of animated or interactive objects on the top window. While scrolling, control can shift focus to the object, a picture or video, and interrupt the action of scrolling down. This can sometimes result in the end user accidentally activating Expose. Yeah, that would be me.