Postgresql.conf group ownership changed automatically

Hi,
We have linux host server and use docker container in it for
hosting of postgresql 12 version database. Its postgresql.conf file
ownership was postgres:postgres in container server and it was working fine.

Recently I did a timezone parameter change in the postgresql.conf file and
then did pg_reload_conf() from pgadmin. Now, postgresql.conf file group
ownership has changed automatically to some numeric number which is not
available in /etc/group too. However, file ownership is postgres only and
db is working.

I can do "chgrp postgres postgresql.conf" online but as it is a
containerized database it may be sensitive to such changes so I want to be
sure that this change would not adversely impact the container.

Please let me know if someone encountered such an issue and solution to it.

Thanks
Mukesh