When using the Turnitin for iPad® app to grade a Turnitin LTI (external tool) assignment created through Canvas, there is a known issue with the grade not displaying in the Canvas gradebook.
At this time, the iPad app doesn't send a grade to the Canvas gradebook due to how the LTI specification is designed. Turnitin will only send a callback when the grade is updated through the LTI assignment. Our integrations team will work with Canvas to improve this with a later version of the LTI integration.
As a work-around, we suggest that Instructors grade submissions made to Canvas LTI assignments from a desktop computer or laptop, rather than using the iPad app when using the Canvas gradebook.