Pull Code operation

GROMACS version: 2016

I wanted to perform the pull code applied in this paper “https://pubs.acs.org/doi/10.1021/acs.jpcc.7b00484”, but I was not successful because the atoms of Mo and S of MoS2 slabs dispersed in the simulation box although I defined the posre. itp for the upper layer which would be exfoliated. I considered the other layers fixe and freeze.
does anyone have experience with this subject?