Comment 4 for bug 1671540

Software Uodate window disappears frequently in my system too. I'm running Ubuntu 16.04.02, Unit-7.4.0 in Zbook-G3 laptop with Nvidia-372.13 binary driver. No matter what you the icon only occasionally flickes in the menu, but no window appears.

Killing the "update-notifier" process manually and starting it again from the HUD does not help.

Also, might be related, starting "update-manager" from CLI produces following error while the icon again flicker, but no window disappears:

/usr/bin/update-manager:28: PyGIWarning: Gtk was imported without specifying a version first. Use gi.require_version('Gtk', '3.0') before import to ensure that the right version gets loaded.
  from gi.repository import Gtk
/usr/lib/python3/dist-packages/UpdateManager/UnitySupport.py:29: PyGIWarning: Dbusmenu was imported without specifying a version first. Use gi.require_version('Dbusmenu', '0.4') before import to ensure that the right version gets loaded.
  from gi.repository import Dbusmenu, Unity
/usr/lib/python3/dist-packages/UpdateManager/UnitySupport.py:29: PyGIWarning: Unity was imported without specifying a version first. Use gi.require_version('Unity', '7.0') before import to ensure that the right version gets loaded.
  from gi.repository import Dbusmenu, Unity