Ligament property for the full-body squat Model

Hi,

I'm investigating the effect of changes in stiffness of ligaments on knee joint stability in squat motion.

So, I added 17 ligament bundles and gave ligament property on a full-body squat model in AMMR model folder based on the reference.

This is the model ligament properties.


And I checked the model worked well.

But, when I increased some ligaments properties of 2500N to 2530N, the model didn't work. Kinematic analysis works well, while inverse dynamic analysis turns and stops in the middle of the step.
The stiffness value increased by 1.2%, but I am not sure why the analysis stops in step 9/16. Conversely, even if I reduce the stiffness value, inverse dynamic analysis stops in the middle.

This is the error code and message.

WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
WARNING(OBJ1) : Ligaments2.any(4) : PLine : Number of allowed iterations during contact penetration removal has been exceeded in line segment 0. Final error at time 0.9 : 1.33321e-08 rel error, 3.89055e-07 abs error
ERROR(OBJ.MCH.MUS4) : Squat_MA_MOD.mainI2.any(102) : Study.InverseDynamics : Muscle recruitment solver : solver aborted due to singular KKT matrix
9) ...Inverse dynamic analysis terminated
ERROR(OBJ.MCH.KIN3) : Squat_MA_MOD.mainI2.any(102) : Study.InverseDynamics : Kinematic analysis failed in time step 9

I changed the ligament stiffness of Ligaments2.any.

Has there been a case where a slight change in the stiffness value affected the progress of the inverse dynamic analysis?

Thanks,