"No such schema 'org.gtk.Settings.Debug'" error upon trying to activate GTKInspector shortcuts

thank you for your bug report, the schemas is part of libgtk-3-dev you need to install that binary

I already have that package installed.

So clearly it does not properly provide the schemas in that package and that is probably where the bug is.

the Ubuntu package has that schemas and works fine, you might have an issue with the Ubuntu GNOME ppa then, closing the Ubuntu side and letting the GNOME remix team handle it instead

The schemas are definitely there in the libgtk-3-dev package from the ppa, it is after all a direct backport/copy from the xenial archives.

Are you sure that package is installed?

@Tim, well, when I run the command "apt-cache policy libgtk-3-dev" I get this output:

    libgtk-3-dev:
    Installed: 3.18.5-1ubuntu2~wily1
    Candidate: 3.18.5-1ubuntu2~wily1
      Version table:
     *** 3.18.5-1ubuntu2~wily1 0
            500 http://ppa.launchpad.net/gnome3-team/gnome3-staging/ubuntu/ wily/main amd64 Packages
            100 /var/lib/dpkg/status
         3.16.7-0ubuntu3 0
            500 http://archive.ubuntu.com/ubuntu/ wily/main amd64 Packages

Do you have this file?

/usr/share/glib-2.0/schemas/org.gtk.Settings.Debug.gschema.xml

If so then try:
sudo glib-compile-schemas /usr/share/glib-2.0/schemas/

I have that file upon running the command which you provided it now has the Debug section!

That command should be run automatically when you installed libgtk-3-dev (or any other package containing schemas). So I guess the real question here is why it did not trigger it when you installed. I am curious if it is reproducible can you try removing libgtk-3-dev (check the schema key has gone away), then reinstall libgtk-3-dev and check if the key is back (without that command)

@Tim, well, when I remove (or even purge) that package the Debug section still remains, though all of its information is gone and only one setting remains... So I'm not sure if it is a fair test if some of it stays... But upon reinstalling that package again the section does fully come back.