Hi, I took a look at your blueprint and my
guess is that the error was probably caused by a mismatch between the coupler positionings. Maybe relative to each other, or relative to the offsets in the actual coupler 3D.
Your coupler attachment values look like you used the editor's preview tool to move the couplers into place, which from own experience I'd recommend against as that results in those extremely "unround" numbers that are hard to check for errors. It takes some getting used to, but I think it's better to add the coupler attachment values by hand, using measured data in your 3D program as your starting point.
Assuming you're using a coupler similar to the Kuju/DTG North American knuckle couplers, then there will be an offset of the coupled and uncoupled models' pivots on the length axis of exactly 0.75 meters. This must be reflected in your blueprints: the offset between coupler pivot and front/back pivot must also be that 0.75 on each end of the car, and the difference between collision length and distance between front/back pivots must also match 0.75. I hope I got all of this right.
Or probably a similar formula if your coupler is using a different pivot offset, but I haven't tried that myself yet.
I hope this makes sense.
Cheers,
Michael