There is an issue with the collisions at the edge of terrain segments, causing a fast moving object to jump when crossing to another segment.
Presumably, in a single step, the body will penetrate the terrain, and at the edge of a segment, it collides with the edge, rather than just the surface.
Though someone may have a better idea for a fix (like custom collision detection/response on the edge of a segment, or limiting a bodys drop on terrain)
I have an idea for a little workaround
Extend each segment by 1 square on each side, but slightly lower than the vertex it would be matching
This should still leave us with a slight “bump” when crossing segments, but hopefully much less.