Suggestion would be to have a “c” program that used getgrnam, to print the member list on the server and on the node, to see that results match with respect users and their groups.
As per the qsub man page
List of group names. Job is run under a group name from this list. Sets job’s group_List attribute to g_list. Default: login group name of job owner.
Format of g_list:
Only one group name may be specified without a host name. Only one group name may be specified per named host. The server on which the job resides will
select first the group name whose host name is the same as the server name. Failing that, the next selection will be the group name with no specified
hostname. The group names on the server and execution hosts must be the same.
Under Windows, the primary group is the first group found for the user by PBS when it queries the accounts database.