I agree this escape lader is nicely designed.

About simulating its deformation with Sweet Home 3D, Daniels118 was right to mention that the shapes bound to eachother must form a tree.

I suspect that the "sweethome3d_opening_on_hinge_1_and_sweethome3d_opening_on_hinge_2_1" as set on the right upright was the culprit

This kind of syntax is not correct: at the left of _and_ separator, there must be a text starting by sweethome3d_rail_, sweethome3d_hinge_ and sweethome3d_ball_, i.e. the name of the shape used as an axis or a ball.
At the right of _and_ separator, there must be a text starting by sweethome3d_opening_on_rail_, sweethome3d_opening_on_hinge_ or sweethome3d_arm_on_ball_ which will reference the rail, hinge or ball to which the shape you're naming is attached to.
You should probably use a name like sweethome3d_opening_hinge_3_and_sweethome3d_opening_on_hinge_2_1 and unfortunately, don't hope that some two way constraints can be applied between shapes.