Plus 1.......id say your knot is not uniformly tightened ,or is cocked off to the side changeing the pull from center to side.
Hrm, this leads me to ask 'what knot?'

I never tied a knot in the channel with my whoopie slings. I just ran one end through, then did a hitch by running the other end (the adjustable end) of the whoopie slings through the eye loop and cinched it down.