By default, when Ubuntu.pm creates user accounts in the 'reserve' function, it does not set the user id for the account. The user account would be created with uid 1000
My work-around was to replace
my $useradd_string = "/usr/sbin/useradd -d /home/$user_name -m -g admin $user_name";
my $user_uid = $self->data->get_user_uid();
my $useradd_string = "/usr/sbin/useradd -d /home/$user_name -m -u $user_uid -g adm $user_name";
Please note that these updated lines also contain a fix for the 'admin' group not existing, but rather the 'adm' group.