This is what I get when running gufw from terminal as asked and reproduce bug... ?????????@?????????:~$ gufw
(gufw.py:2041): Gtk-CRITICAL **: gtk_tree_path_to_string: assertion 'path != NULL' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_value: assertion 'iter_is_valid (iter, list_store)' failed /usr/share/gufw/gufw/view/guiGufw.py:52: Warning: g_object_set_property: assertion 'G_IS_VALUE (value)' failed Gtk.main() /usr/share/gufw/gufw/view/guiGufw.py:52: Warning: g_value_unset: assertion 'G_IS_VALUE (value)' failed Gtk.main() (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_value: assertion 'iter_is_valid (iter, list_store)' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_path: assertion 'iter->stamp == priv->stamp' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_tree_path_to_string: assertion 'path != NULL' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_value: assertion 'iter_is_valid (iter, list_store)' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_value: assertion 'iter_is_valid (iter, list_store)' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_path: assertion 'iter->stamp == priv->stamp' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_tree_path_to_string: assertion 'path != NULL' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_value: assertion 'iter_is_valid (iter, list_store)' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_value: assertion 'iter_is_valid (iter, list_store)' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_get_path: assertion 'iter->stamp == priv->stamp' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_tree_path_to_string: assertion 'path != NULL' failed (gufw.py:2041): Gtk-CRITICAL **: gtk_list_store_iter_next: assertion 'priv->stamp == iter->stamp' failed (gufw.py:2041): Gtk-CRITICAL **: /tmp/buildd/gtk +3.0-3.14.5/./gtk/gtktreeview.c:5495 (gtk_tree_view_bin_draw): assertion `has_next' failed. There is a disparity between the internal view of the GtkTreeView, and the GtkTreeModel. This generally means that the model has changed without letting the view know. Any display from now on is likely to be incorrect.
