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I have Loki installed on my laptop and desktop. Appcenter works fine on my laptop, but it doesn't on my desktop. It doesn't show any updates, that tab is empty. I can browse and search for software, but everything has an "install" button, even programs that are already installed. Pressing install results in either Appcenter freezing, or displaying "waiting" forever.
I can install, remove, and update things just fine from the terminal. I've tried uninstalling and reinstalling appcenter, updating apt, and everything else I could find here on Stack Exchange. Here's the empty update tab, no updates or current software is displayed. According to Appcenter, Pantheon-files is not installed (it is)