You are pretty much close.
I wish I could see the locks location. Looks like you have another one in the middle somewhere.
But regardless, there is only one reason for snapping out - forcing/moving cable against law of physics.
Take a look at 0:32. The tube is about to fold because it has nowhere to go.
75% of original size (was 671x19) - Click to enlarge
The main line (after the fold point and up) has to be moved outward a bit to release tension and pressure (that is what would have happened in real life).
Again, I am not sure where the locks are, their position, angle and shape. And also camera angle does not allow to see whole picture.
There are other ways to operate/tweak cable/tube - external rigid objects animated on the fly to push it externally one way or another.
You can sure use weight map to permanently lock one end. And it might or might not help. Since the tension is still there, it might just force the tube to fold.
Bottom line - while *driving* the tube, you should watch for tensions and release it where necessary. Tube has to be *relaxed* and natural during whole animation.