AppCenter doesn't show updates or install anything [duplicate]

Question

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)

Answer 1

The elementary team has issued instructions on how to fix this (see https://medium.com/elementaryos/important-update-released-501c9d9f28b). Apparently there was a mismatch between AppCenter and packagekit.

sudo apt update

sudo apt install packagekit

Answer 2

I had this same issue and this helped:

1.) remove the eOS repo:

sudo add-apt-repository --remove ppa:elementary-os/daily

2.) update/upgrade repos

sudo apt-get update && sudo apt-get upgrade

3.) reboot

4.) add the repo back

sudo add-apt-repository ppa:elementary-os/daily

5.) update/upgrade repos

sudo apt-get update && sudo apt-get upgrade

this should upgrade the AppCenter app as well and it should work.

If not, try rebooting - it might help. For me the AppCenter sometimes works, sometimes doesn't... I just reboot and it's probably fine after the next boot.