Terry,
The graphcanvas plugin also stopped working fully after the switch from python 3.5.2/PyQt5 v5.7.0 to python 2.7.13/PyQt4.
The 'Graph' tab display was blank, and I had to run 'graph-toggle-autoload' to display the graph and then reload.
I raise this as a new issue but it may be related to the
Bookmarks pane disappears issue as both plugins use c.db and subject to the pickle protocol.
Regards
Lewis