Comment 19 for bug 1637180

some guessing work/suggestion here, resize_to_standard_width() does

        ctx = self.get_style_context()
        size = ctx.get_property("font-size", Gtk.StateFlags.NORMAL)

that's likely to create a "changed" event and trigger the loop

the usual way to fix those is to call
GObject.signal_handler_block() before those lines
and
GObject.signal_handler_unblock()
after the lines

you just need to get the right handler in the function to do that