GLib-GObject-CRITICAL **: g_object_set: assertion 'G_IS_OBJECT (object)' failed

My syslog is filling up with these lines:

localhost org.gnome.Shell.desktop[3485]: (gnome-shell:3485): GLib-
GObject-CRITICAL **: g_object_set: assertion 'G_IS_OBJECT (object)'
failed
localhost org.gnome.Shell.desktop[3485]: (gnome-shell:3485): GLib-
GObject-CRITICAL **: g_object_set: assertion 'G_IS_OBJECT (object)'
failed
localhost org.gnome.Shell.desktop[3485]: (gnome-shell:3485): Clutter-
CRITICAL **: clutter_layout_manager_get_child_meta: assertion
'CLUTTER_IS_LAYOUT_MANAGER (manager)' failed

My system is:

Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.2 LTS
Release:	16.04
Codename:	xenial

apt-cache policy gnome-shell
gnome-shell:
  Installed: 3.20.4-0ubuntu2~ubuntu16.04.1
  Candidate: 3.20.4-0ubuntu2~ubuntu16.04.1
  Version table:
 *** 3.20.4-0ubuntu2~ubuntu16.04.1 500

The theme I'm using is 'Traditional Ok' Icons are Gilouche. Here's one
seconds worth of output in pastebin - https://pastebin.com/9yMTQJi9 Cou
ld this be simply be caused by the theme I'm using?

Chris

-- 
Chris
KeyID 0xE372A7DA98E6705C
31.11972; -97.90167 (Elev. 1092 ft)
08:20:29 up 11:26, 1 user, load average: 0.92, 0.75, 0.75
Description:	Ubuntu 16.04.2 LTS, kernel 4.4.0-71-generic

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