Modified amino acid disconnects after docking

I ran a protein protein docking and the modified amino acid of the first molecule(res 73) gets disconnected from the amino acids adjacent to it(res 72 & 74) after the docking.The link to my job is :

Do you have any idea why this happens?

This is normal behaviour since the modified amino acid (probably defined as HETATM in the PDB) can not be linked to the other amino acids. For a list of supported modified amino acids refer to: