We have noticed a rare issue regarding multiple submissions appearing for a user in the assignment inbox. Basically it looks like the student has submitted twice. By refreshing the Inbox Data, the earliest submission dissapears but when you exit the assignment and go back into the assignment, it appears again.
We have noticed this on our LTI 1.3 integration to Turnitin.

When asked TII support have advised...
 

Multiple submissions to an assignment made by the same student may occur if the student has two active login sessions at the time of submission and has attempted to submit the same paper in both login sessions - e.g., a student has two separate browser tabs open and submits the same paper in both tabs within the same timeframe.

This is not a supported workflow and can result in multiple submissions to the same assignment.
I have asked our Guides Team to add a public facing help page on this behavior for the students to be aware.

Lastly, I have submitted feedback to our Product and Marketing Teams for further consideration to add a section on the user page to add feedback to our Turnitin product. Although not all requests can be implemented, we believe in listening to what our users request and greatly appreciate suggestions on how to improve our service and products to provide a better user experience.