systemd-cgls command prints blank output for user.slice

Issue

• RHEL 7 hosts don't show user.slice for user sessions.
• systemd-cgls command prints blank output for user.slice.
• When users login, as shown in the example below, their session does not show up under systemd-cgls user.slice.

[root@xls1 ~]# grep testit /etc/passwd
testit:x:123:123::/home/testit:/bin/bash

[root@xls1 ~]# systemd-cgls /user.slice
/user.slice:
(Blank output)