Same Bug for Me
I confirm that I had the same problem with four-finger gestures working initially but then not working after I set three-finger dragging. Toggling the Mission Control/App Expose settings to 3-finger and back to 4-fingers fixed the problem.
Also, I noticed that after fixing this, 3-finger dragging again didn't work. I had to go back in and recheck the checkbox for it.
Also also: I'm noticing that the 4-finger Mission Control gesture sometimes gets stuck mid-animation so I only see a couple of overlapping windows in the center of the screen.