Periodicity problem

GROMACS 2018:
GROMACS modification: No
After running gromacs calculation for 100ns I got the md simulation video in which the protein structure is distorted. Kindly look into the files and tell me the solution.Upto NPT the protein was not distorted.

Please read https://manual.gromacs.org/current/user-guide/terminology.html#periodic-boundary-conditions and https://manual.gromacs.org/current/onlinehelp/gmx-trjconv.html. Hopefully that will help you.