offset-anchor appears corrected in Chrome Canary 66 with the Experimental Web Platform Features flag enabled
CSS Motion Path (Offset Path) has five properties in the current spec. Path, Rotation, and Distance have all had implementation in Chrome since v46, but the two newer properties are just being introduced as the spec is evolving.
offset-anchor changes which point on the element follows the path (by default it is the center). Seems incorrect in its first implementation in Chrome Canary 58 or 59