GNOME Software / PackageKit仅列出已安装的软件包

我注意到Fedora 24安装上的GNOME软件仅显示已安装的软件包（即使在“精选”和“编辑精选”部分中）。我也无法搜索要安装的新软件包。这是“图形”类别的屏幕截图。在左侧，它仅显示已安装的软件包。在右侧（从另一台计算机），它显示正确的列表：

I found out that GNOME Software is a frontend for PackageKit, so I tried to use the CLI (pkcon). However, it also doesn't find most of the programs. For example, I wanted to search for Shotwell using the CLI. This is the output:

[user ~]$ pkcon search name shotwell
Searching by name             [=========================]
Finished                      [=========================]
[user ~]$

On the other computer, pkcon finds the package:

[user ~]$ pkcon search name shotwell
Searching by name             [=========================]
Starting                      [=========================]
Finished                      [=========================]
Available    shotwell-0.23.5-1.fc24.i686 (updates)    A photo organizer for the GNOME desktop
Available    shotwell-0.23.5-1.fc24.x86_64 (updates)    A photo organizer for the GNOME desktop
Available    shotwell-0.23.1-1.fc24.x86_64 (fedora)    A photo organizer for the GNOME desktop
[user ~]$

How can I fix PackageKit to find all packages again?

Edit: Output of dnf repolist:

repo id                    repo name                                      status
Dropbox                    Dropbox Repository                                  4
*fedora                    Fedora 24 - x86_64                             49.722
google-chrome              google-chrome                                       3
rpmfusion-free             RPM Fusion for Fedora 24 - Free                   352
rpmfusion-free-updates     RPM Fusion for Fedora 24 - Free - Updates         277
rpmfusion-nonfree          RPM Fusion for Fedora 24 - Nonfree                 89
rpmfusion-nonfree-updates  RPM Fusion for Fedora 24 - Nonfree - Updates      127
*updates                   Fedora 24 - x86_64 - Updates                    9.817