bastien@data-dev4:~$ LANG=C gnome-shell --replace
      JS LOG: IBus version is too old
Window manager warning: Log level 16: Unable to register authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: An authentication agent already exists for the given subject
    JS ERROR: !!!   Exception was: Polkit.Error: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: An authentication agent already exists for the given subject
    JS ERROR: !!!     message = '"GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: An authentication agent already exists for the given subject"'
    JS ERROR: !!!     fileName = '"/usr/share/gnome-shell/js/ui/components/polkitAgent.js"'
    JS ERROR: !!!     lineNumber = '329'
    JS ERROR: !!!     stack = '"0 anonymous()@/usr/share/gnome-shell/js/ui/components/polkitAgent.js:329
1 wrapper()@/usr/share/gjs-1.0/lang.js:204
2 anonymous("name" = ""polkitAgent"")@/usr/share/gnome-shell/js/ui/components/__init__.js:56
3 wrapper(""polkitAgent"")@/usr/share/gjs-1.0/lang.js:204
4 anonymous("name" = ""polkitAgent"", 1, [object Array])@/usr/share/gnome-shell/js/ui/components/__init__.js:22
5 anonymous()@/usr/share/gnome-shell/js/ui/components/__init__.js:21
6 wrapper()@/usr/share/gjs-1.0/lang.js:204
7 anonymous()@/usr/share/gnome-shell/js/ui/components/__init__.js:13
8 wrapper()@/usr/share/gjs-1.0/lang.js:204
9 anonymous()@/usr/share/gjs-1.0/lang.js:145
10 anonymous()@/usr/share/gjs-1.0/lang.js:239
11 start()@/usr/share/gnome-shell/js/ui/main.js:150
12 <TOP LEVEL>@<main>:1
"'
Window manager warning: Log level 32: Execution of main.js threw exception: Polkit.Error: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: An authentication agent already exists for the given subject
bastien@data-dev4:~$