The only analytical solution I have for the displacement is just the total stretch value from a formula. But I can try different BC configurations (so far none helped) later and share the screenshots of the corresponding deformed shapes.
I also suspect that. After all, if stiffness is too high, it’s almost always a fault of overconstraining BCs. Maybe I will try with symmetry in a 3D model and try to figure out the assumptions made by the author of the original paper.