Lerping like that is not framerate independent, and that might be the problem. Maybe try use this spring module to interpolate it? Example:
-- in constructor
local horizontalSpring = Spring.new(0)
horizontalSpring.s = 15 -- speed
horizontalSpring.d = 1 -- damping, 1 is smooth, lower the more "bouncy"
self.horizontalSpring = horizontalSpring
-- in a loop:
horizontalSpring.t = rad(horizontalDegrees)
self.horizontalMotor6d.C0 * cFrameAngles(0, self.horizontalSpring.p, 0)
--repeat for vertical
I dunno if it will help, we’ll see