Sorry I could not build a reproducible test case.
This issue is spot when I am editing glyph. My edit workflow includes 1) constantly switching between point mode and contour mode and 2) editing the transformations position for a group of points.
When this issue kicks in, FC pauses for a few noticeable milliseconds and then it will randomly shift the contour to a surprising position.
I have not seen this issue before 3073, things are working flawlessly in 3072, so it is likely a regression introduced in the last release.