level sequence "path" track introduces jittery movement in "play" mode

I have an animated skeletal mesh moving along a spline using the “path” track inside a level sequence. In “simulate,” the actor behaves as expected, smoothly moving along the spline. But for some reason, when in “play” mode, the actor jitters up and down the Z axis about 10 units every frame during the path animation. I’ve tried adding a “zero” keyframe in the transform track before the path, no use. I’ve tried using an empty actor as an intermediary “parent” to attach to, no use.

Why does this act glitchy only in “play” mode and how do I get around it?