Multi-seat works perfectly up to the point which I decribe below.

There are existing users who do not login who automatically appear to
login onto the workstation.
(no remote services -- it's not a compromised system)

loginctl
SESSION  UID USER    SEAT   TTY
   14518    0 root
    8901 1000 userA   seat0
     c14  131 lightdm seat0
     c33  131 lightdm seat-1


Even after clearing the logged-in users (there's only about 2 or 3 users
on this system.. ) , with loginctl terminate-user ...  a user or two
then re-appear again...

ps shows gvfs things.

I looked at timers with systemctl list-timers and disabled/stopped any
of them.

I also tried to look at timers with user accounts using, "systemctl
--user" list-timers and couldn't find anything under there.

I wonder what is "triggering" these processes...

it must be a bug lightdm.

/etc/lightdm/lightdm.conf
----------------
[Seat:seat0]
logind-check-graphical=true
type=xlocal

#xserver-config=/etc/X11/xorg.conf.intel_seat0
#note: debian's current Xorg (in this system), manpage does not indicate
-seat seat_id but Xorg --help shows it is available

xserver-config=/etc/X11/xorg.conf.seat0
xserver-command=/usr/bin/Xorg -nolisten tcp -layout layout_seat0 -seat
seat0 -novtswitch


[Seat:seat-1]
logind-check-graphical=true
type=xlocal

xserver-config=/etc/X11/xorg.conf.seat-1
xserver-command=/usr/bin/Xorg -nolisten tcp -layout layout_seat-1 -seat
seat-1 -novtswitch
-------------

I provided xserver-config for the two seats, there's nothing special I
can find which can be triggering this...

Despite the multiple ghost-logins, I am able to login via lightdm with
the already listed users shown with loginctl list-users.