(translated from the German version, so wording may be inaccurate)
Go to
XFCE Menu -> Settings -> Settings -> Startup and Sessions -> Programs started automatically
and activate "Policykit Authentication Agent".
Maybe there is something similar in LXDE.
But the question remains:
Why did this deactivate itself ?
At least on my Laptop, I am 100% sure that I never, ever opened this part of the settings.
I have a soluton, at least for XFCE:
(translated from the German version, so wording may be inaccurate)
Go to
XFCE Menu -> Settings -> Settings -> Startup and Sessions -> Programs started automatically
and activate "Policykit Authentication Agent".
Maybe there is something similar in LXDE.
But the question remains:
Why did this deactivate itself ?
At least on my Laptop, I am 100% sure that I never, ever opened this part of the settings.