There have been a few instances recently where people have pointed out that GNOME Software marks some apps as not free software when they are. This is a bug in the appdata files provided by those applications, which typically includes something like
<project_license>GPL-3.0+ and CC-BY-SA-3.0</project_license>
This is generally an attempt to list the license of the code and of the documentation. However, the resulting SPDX expression means to apply the most restrictive interpretation of both licenses. As a result, the expression as a whole is considered not free software (CC-BY-SA-3.0 is not a free software license as per the FSF or OSI lists).
Instead, those apps should probably just list the ‘main’ license for the project:
and document the license for their documentation separately. As far as I know, the appdata format doesn’t currently have a way of listing the documentation license in a machine readable way.
If you maintain an app, or want to help out, please check the licensing is correctly listed in your app’s appdata.
There’s an issue open against the appdata spec for improving how licenses are documented in future — contributions also welcome there.
(To avoid doubt, I think CC-BY-SA-3.0 is a fine license for documentation; it’s just problematic to include it in the ‘main’ appdata license statement for an app.)