Current v54 release has GTK 2 symbols embedded in libcef.so and it results in GTK error when running GTK 3 example:

Gtk-ERROR **: GTK+ 2.x symbols detected. Using GTK+ 2.x and GTK+ 3 in the same process is not supported

Reported on the CEF Forum #14596 and later created CEF Issue #2014.

Additionally there might be an another issue in setup.py which links to such libraries:

'gobject-2.0',
'glib-2.0',
'gtk-x11-2.0',

Looks like 'gtk-x11-2.0' is GTK 2.0 and you cannot use GTK 2 and GTK 3 in the same process. This didn't cause issues in v53 release in the GTK 3 example, however this might be an issue if you freeze app, I don't know, maybe. Further testing is required.