I hear that! Keep safe and health 
I don’t think that’s from flexing… at least it doesn’t look like my flexing issues. It’s weird how the angle changes when the carriage goes up and down I haven’t seen that before and I’m not sure what would cause that.
Well, I’ll work on cutting some new Y-plates out of 3/4 inch plywood and see if that improves the situation.
I think your roller bearings are loose. Try to tension them to touch the tubes again.