Probably way off base here but you never know… How fast are you running between waypoints?
I’ve found that even when payload and COG are set correctly, if I manually slow down the robot it will shake at times. Odd that it will shake going slower, but the tech we usually have at our shop said, yes, if you slow it down it may shake a bit.
And having that much weight out at the end of reach is probably not helping. If you’re well within your speed parameters, you might just try speeding it up to see if it helps. Again, probably way off base but it’s all I got! 