On my lab systems, the automatic updates were failing because of the problems with ipod libraries from EPEL being in the way. It turns out that was a good thing, because when I "fixed" it, a massive set of packages was updated, including the new gtk3.
These packages are the ones causing problems, I think.
gtk3-3.22.10-4.el7.x86_64 gtk3-devel-3.22.10-4.el7.x86_64
In the release notes, there is mention of the "giant icon" problem and how to fix that. We understand that part.
The bad problem I see now is that Emacs and Chromium-browser, which rely on gtk3 don't work properly anymore. In Emacs, the symptom is that the ribbon of buttons under the pull down menu will no longer show. In Chromium, the buttons and other widget things on the top are an ugly yellow distortion.
I've recompiled the Emacs that comes with EL7, as well as 24.5, and the Emacs behaves the same way, no buttons show. The buttons are invisible, but still there. If you click in there, you can get lucky.
Do you see it too in Emacs?
I see some posts that say the Gnome themes don't work any more with GTK and those themes should have been deprecated by the gtk3 packages. I don't think the theme is the cause because I see same problem in both Gnome and XFCE4 desktops. I see it also if I SSH into the machine and run emacs forwarded over X11.
I just realized that on Ubuntu I'm running gtk-3.22.11 with Emacs 24.5 and the icons do show. Maybe there is a change in the compiler flag for Emacs that I'm missing.
pj