Summary: On occasion, a submission will not be retrievable by Canvas. As a teacher I want to be able to re-trigger a failed Turnitin submission from the Turnitin LTI tool.
What's been done: Canvas and Turnitin have discussed this option. We've agreed that this would require work to be done on the Turnitin side; however, to Canvas' knowledge there is no ETA for this.
This would be a really useful feature
For now, as Canvas admin, I can masquerade as a student to submit if have to ... ok when only have a few to do this for.
I have had a few occasions where this would be useful. But like you mentioned, it really isn't so much a canvas thing. The LTI tool works as it is supposed to. I would definitely petition TII for this.
The Turnitin ticket system has stated they are training their Tier 1 support folks to be able to resynchronize assignemtns that fail to get pushed back to Canvas.
Before it would take many interactions, escalations, and doubts on the TII end...however now they acknowledge this is occurring and you should be able to just ask Tier 1 to resynch. However, currently it takes approx 1-2 weeks to get this done.