Comment 13 for bug 1598298

I run Antergos with MATE 1.16 and GTK 3.20 and have this same problem. I managed to fix it with the following change to indicator.py:
--- indicator.py.old 2016-11-22 09:32:35.572057252 +0200
+++ indicator.py 2016-11-22 09:32:48.745402358 +0200
@@ -316,8 +316,8 @@
         self.status_icon = None
         self.visible = True

- def pos(menu, icon):
- return Gtk.StatusIcon.position_menu(self.menu, icon)
+ def pos(menu, x, y, icon):
+ return Gtk.StatusIcon.position_menu(self.menu, x, y, icon)

         def right_click_event(icon, button, time):
             self.menu.popup(None, None, pos, self.status_icon, 0, time)

Maybe the x and y arguments where made mandatory recently?