[Andrew Blair]

Because in the photos that you call "under load", there is no actual load other than the scissors being lifted, I am assuming that the issue is not simply too much loading, but a problem in the actual design and implementation of the lift. Correct?

As to your issue- As you probably have already figured out, there is a bind or mechanical cinch point which is causing the force needed to raise the scissors to approach that which your mount is failing under. For this type of lift, which I assume is being used only for tubes, your bent mount should be plenty strong enough, when it's all resolved.

My thoughts are that you are not allowing the lead screw to move the proper amount laterally, based on the look of the lift. It appears that you've anchored one side of the lift, and are allowing the other side to move on rollers. It also looks like there is provision for angular change at the point that the screw connects to the loft, but your motor is tied fairly statically to the bar. It cannot rotate to account for angular change, while the connection point is shifting laterally. So , you bind at the point where the motor starts to want to rotate, but cannot. Or maybe I'm looking at your lift all wrong.