This time, after the homework had closed in Webwork, the instructor decided one of the questions was out of scope. She marked it as correct. This changed a few people's grade, but the grades changed in Webwork, NOT in Canvas.
I've tried the following....
* changing the open dates in Webwork
* changing the open dates in Canvas
* going through the homework assignment as one of the affected students
* changing the LTIMassUpdateInterval to 3600 (1 hour) to see if it will autoupdate
* logging in as a test user in Canvas, and doing the homework myself, to see if the grades passback. (They do.)
We are using it in LTIGradeMode = "homework" and LTIGradeOnSubmit = 1;