Hey Sam and Dmitry, I've seen that issue as well : try to install and enable gnome-power-manager in your session. I know it sucks but it seems that gnome-power-manager is mandatory now even on desktops... If you run it from a command line it will say that it won't do anything because it's not running on a laptop but it seems it needs to run in order for gnome-panel to work properly.
Josselin maybe you can advise us on a workaround ? It seems a bit stupid to have to run an additional process which says that it won't do anything... Let me know if this solve the issue for you too. LeTic
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