I have a theory that maybe a contributing factor to the machine struggling in the corners is how the anchor points are laid out. If they are laid out so that going to the corner leads to a situation where three belts are pulling one way and only one is pulling the other way it could be hard for the one belt that is fighting 3 to keep up/
I was wondering if maybe your setup looked significantly different than the one in this thread, but it doesn’t look too different:
