systemd user instance not working in only one account, XDG_RUNTIME_DIR not being set

[Chandler <admin@xxxxxxxxxxxxxxxxxx>]

systemd has been working great here, system-wide as well as in all user
instances except one.  I'm not exactly sure what all the steps are in
the process to get a systemd user instance running.  The directory
/run/user/$UID was not being created, though.

I made some progress by running `systemctl start
user@<username>.service` and the /run/user/$UID was created.

`systemctl --user status` returns `Failed to connect to bus: No such
file or directory`.  XDG_RUNTIME_DIR is not being set, but a command
like `XDG_RUNTIME_DIR=/run/user/$UID systemctl --user status` runs
successfully, so I think it's down to this last piece.

Apparently XDG_RUNTIME_DIR is related to PAM?  I don't think I should
have to change PAM settings or anything like that since systemd is
working fine already in the other user accounts.  I couldn't find any
info on how to fix this part... What do you experts think?

The computer is stuck with CentOS 8 unfortunately and old v239 of
systemd, but I don't think that's the issue either since systemd is
working fine in all other cases.  I just wanted you to know in case
there are some deprecated commands or config needed to fix the problem.

Thanks