Upon login to the desktop, the following popup appears:

Plugin "Power Manager Plugin" unexpectedly left the panel, do you want to restart it?

The plugin restarted more than once in the last 60 seconds. If you press Execute the panel
will try to restart the plugin otherwise it will be permanently removed from the panel. 

When I try to run "xfce4-power-manager" through the terminal, I get:

(xfce4-power-manager:16086): libupower-glib-WARNING **: 12:03:24.189: Couldn't connect to proxy: Error calling StartServiceByName for org.freedesktop.UPower: Launch helper exited with unknown return code 127

(xfce4-power-manager:16086): GLib-GObject-CRITICAL **: 12:03:24.200: invalid (NULL) pointer instance

(xfce4-power-manager:16086): GLib-GObject-CRITICAL **: 12:03:24.200: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

(xfce4-power-manager:16086): GLib-GObject-CRITICAL **: 12:03:24.200: invalid (NULL) pointer instance

(xfce4-power-manager:16086): GLib-GObject-CRITICAL **: 12:03:24.200: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

(xfce4-power-manager:16086): GLib-GObject-CRITICAL **: 12:03:24.200: invalid (NULL) pointer instance

(xfce4-power-manager:16086): GLib-GObject-CRITICAL **: 12:03:24.200: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

(xfce4-power-manager:16086): libupower-glib-CRITICAL **: 12:03:24.200: up_client_get_devices_full: assertion 'UP_IS_CLIENT (client)' failed
zsh: segmentation fault  xfce4-power-manager

According to this thread, it seems that "dbus" service not running is the cause: https://forums.gentoo.org/viewtopic-p-8786796.html?sid=8cc6d2033d0521bbb7cf242d9fbabb91

However, the dbus service seems to be already running in both my root and user tree when I check with "66-intree":

Name         : root
Initialized  : yes
Enabled      : yes
Starts after : None
Current      : yes
Allowed      : root
Symlinks     : svc->source db->source
Contents     : /
               ├─(736,Enabled,classic) wpa_supplicant-log
               ├─(734,Enabled,classic) openntpd-log
               ├─(730,Enabled,classic) ttz@ tty3-log
               ├─(732,Enabled,classic) ttz@ tty3
               ├─(735,Enabled,classic) openntpd
               ├─(0,Enabled,classic) wpa_supplicant
               ├─(762,Enabled,longrun) dbus-log
               ├─(767,Enabled,longrun) dbus
               ├─(761,Enabled,longrun) networkmanager-log
               ├─(777,Enabled,longrun) networkmanager
               ├─(763,Enabled,longrun) consolekit-log
               └─(778,Enabled,longrun) consolekit

Name         : base
Initialized  : yes
Enabled      : yes
Starts after : None
Current      : yes
Allowed      : hyperspace
Symlinks     : svc->source db->source
Contents     : /
               ├─(972,Enabled,longrun) dbus-session@ hyperspace-log
               ├─(971,Enabled,longrun) pulseaudio-log
               ├─(980,Enabled,longrun) pulseaudio
               ├─(up,Enabled,oneshot) xdg-user-dirs
               └─(979,Enabled,longrun) dbus-session@ hyperspace

How would I resolve this the s6+66 way?