Adding an extra space at the end of the value of baseurl in rpm repo file causes PackageKit to fail with the symptoms that pkcon, GNOME software and any other softwares that depend on it fail to resolve and install packages.
example rpm repo that causes the bug,/etc/yum.repos.d/fedora.repo
baseurl=http://192.168.1.9/repo/os <- extra space
repo that works
baseurl=http://192.168.1.9/repo/os<- no extra space
yum/dnf is able to handle this so I think it is a bug of PackageKit that forgot to trim the whitespacse at the end of the value of baseurl, possibly other fields too.
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.