Seems that redhat-config-users sometimes makes duplicated gid
in /etc/group file.
I can not tell exactly when this happen,
but seems it somehow related to afact whether there exist
a separate group with gid >500
so uid and gid of a user cerated are different.
At some circumstances the data put into /etc/group may be invalid
I can't duplicate this with redhat-config-users-1.1.1-2, which is what we
shipped in 8.0. Can you try that version and see if this still happens?
Closing due to lack of information.