GLib-CRITICAL **: g_variant_new_string: assertion `string != NULL' failed

Startup is very slow and xsession errors give the following message:

openConnection: connect: Bestand of map bestaat niet
cannot connect to brltty at :0
xfce4-settings-helper: Another instance is already running. Leaving...

(polkit-gnome-authentication-agent-1:1741): GLib-CRITICAL **: g_variant_new_string: assertion `string != NULL' failed

(polkit-gnome-authentication-agent-1:1741): polkit-gnome-1-WARNING **: Failed to register client: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files
** Message: applet now removed from the notification area
** Message: applet now embedded in the notification area
** Message: applet now removed from the notification area
** Message: using fallback from indicator to GtkStatusIcon
** Message: applet now embedded in the notification area
WARNING: gnome-keyring:: couldn't connect to: /tmp/keyring-cb8P5w/pkcs11: Bestand of map bestaat niet
Object::connect: No such slot TimetrackerWidget::updateTabs()
Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave.
QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave.
kbuildsycoca4 running...
kbuildsycoca4(1846) KBuildSycoca::checkTimestamps: checking file timestamps
kbuildsycoca4(1846) KBuildSycoca::checkTimestamps: timestamps check ok
kbuildsycoca4(1846) kdemain: Emitting notifyDatabaseChanged ()
Object::connect: No such slot ktimetrackerpart::updateTime(long,long)
QSystemTrayIcon::setVisible: No Icon set
Object::connect: No such signal TrayIcon::quitSelected()
Object::connect: (sender name: 'Ktimetracker Tray')
ktimetracker(1835)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig:
debconf: DbDriver "passwords" warning: could not open /var/cache/debconf/passwords.dat: Toegang geweigerd
debconf: DbDriver "passwords" warning: could not open /var/cache/debconf/passwords.dat: Toegang geweigerd
debconf: DbDriver "passwords" warning: could not open /var/cache/debconf/passwords.dat: Toegang geweigerd
Object::connect: No such slot TimetrackerWidget::updateTabs()
Object::connect: No such slot ktimetrackerpart::updateTime(long,long)
QSystemTrayIcon::setVisible: No Icon set
Object::connect: No such signal TrayIcon::quitSelected()
Object::connect: (sender name: 'Ktimetracker Tray')

Is this a known issue?