So, I've just been trying out gnome-software and it refuses to update any packages for me. I have my own custom repo in my pacman.conf, with the global "SigLevel = Required DatabaseOptional" and my repo itself set to "SigLevel = Optional TrustAll".
This works perfectly fine in pacman itself, but it appears that gnome-software/packagekit is ignoring these settings. Instead it reports " [dray.be]: unexpected system error" If I try to run the update in gnome-packagekit instead I get a bit more explanation, with the error instead reading "[dray.be]: invalid or corrupted database (PGP signature)" Which would be expected if database signing was turned on, but pacman.conf has it set to optional.
All settings for gnome-software/packagekit are vanilla from the Arch repos. /etc/packagekit/alpm.d/pacman.conf has "Include = /etc/pacman.conf" which I would expect to mean it will use the settings in pacman.conf. But it appears to be ignoring this setting.
There also appears to be no category for pacman backend, or Arch Linux as an OS when filing a bug.
We moved the upstream bugtracker to GitHub a long time ago. If this issue still affects you please re-create the issue here: https://github.com/hughsie/PackageKit/issues
Sorry for the impersonal message, and fingers crossed your issue no longer happens. Thanks.