So I looked at my JLC Big Boy from the early 2000s, assuming mechanically would be very similar to the problem Vision Line Engine. I believe the cylinder I point to in your photo is incorrectly mounted under the boiler.
Here is a pic of my engine making a right hand turn, looking at the right side of the engine. Notice that the steam cylinder pointed to by the Red Arrow and the "Lionel Cylinder" (for making the model function) pointed to by the Yellow Arrow are running parallel, and the Lionel Cylinder end appears to be affixed under the boiler - within blue circle, not coming close to the steam cylinder.
Here are a couple pics of the engine's left side at the same turn position as the right side pic. Notice that the Lionel Cylinder can barely be seen.
So I have to believe that a screw is missing, or some pin is dropped in correct hole, or??? Maybe somebody braver than I handling this big model engine can turn theirs over and get a pic of how the Lionel Cylinder is connected under the boiler.
it appears that the spring is attached to the end hole on the black pipe and the bottom hole on the yellow one.