My first few days, I thought the chain jumped occasionally. Then I noticed that while it happened only when I pedaled hard, it happened only at minimum torque: top dead center.
That's when i switch from pressing with my low foot to pressing with my high foot. When I pedal enthusiastically, my timing may be a little off, slowing the crank for a few milliseconds. Then my high foot drives the crankshaft forward, taking up the slack. The freewheel engages in increments that happen to be about the same as one link in the chain, so it can feel as if the chain jumped a link.