I can verify the problem. The cause is that wwassignment is using older methods for logging events -- unless you set specific legacy flags this means that nothing involving wwassignment is logged. The cron job only updates courses for which there has been recent wwassignment activity (as viewed in mdl_log).
The long term fix will be to update wwassignment to conform to the tools used in moodle 3.x.
For the short term one can force updating the gradebook by editing one or more of the wwassignments in the moodle course and saving the edit.
When they are ready updates will appear on https://github.com/openwebwork/wwassignment
. Pull requests are welcome -- many of you have more expertise in developing moodle modules than I do. I will be happy to help with any issues on the webwork end of the communication.
-- Mike Gage