LTI and Moodle

I'm embedding Moodle quizzes into Canvas and having issues with grades getting sent back to Canvas. (I find that the quiz and question bank system in Moodle is way better than Canvas, which is why I'm doing it this way.)

But grades aren't syncing, which seems to be a somewhat common issue. I noticed that the fail delay gradually creeps up on the scheduled task until it's @ 24 hours.

Found that I'm getting the following message when the task tries to run.

Execute scheduled task: Publish as LTI tool grade sync (enrol_lti\task\sync_grades)
... started 09:11:18. Current memory use 5.7MB.
Starting - Grade sync for shared tool '2' for the course '2'.
Skipping - Empty sourceid for the user '6' in the tool '2' for the course '2'.
Skipping - Empty sourceid for the user '3' in the tool '2' for the course '2'.
... used 4 dbqueries
... used 0.017449855804443 seconds
Scheduled task failed: Publish as LTI tool grade sync (enrol_lti\task\sync_grades),Can not find data record in database table context.
Cron script completed correctly
Cron completed at 09:11:18. Memory used 7MB.
Execution took 0.044808 seconds

This was all working flawlessly last year, once I remembered to turn on the cron job, so I'm a little perplexed why it's stopped. 

Any thoughts or suggestions would be greatly appreciated.