Hi Giorgos,
The issue occurs during the boolean (slicing) operation in 3ds Max. To prevent the segments on the problematic sides from being sliced, I wired an empty segment to the Bottom and Top Inputs of the Generator, which seems to resolve the issue. Also, you can use the 'Scale to Spline Section' macro to adjust these segments to the size of the clipping areas. I’ve attached the modified version of your scene for your reference. I hope this helps!
Best regards,