This is a strange one!

We are building an LTI 1.3 app to embed some media via Deep Linking, nothing very complicated. 

When we first launch the app we successfully get through OIDC login and the app launches as expected. We can select media, like an image, and do the Deep Link response via POST and it successfully embeds on the page/assignment/etc.

However if we launch again to select & embed another piece of media when we do the Deep Link response via POST we are receiving an error from Canvas:

{"errors":{"data_jwt":[{"attribute":"?data=JWT","type":"already_used","message":"Do not attempt to submit content items multiple times."}]}}

We know for sure that the JWT is different each time we do the POST and we have found no reference to this issue anywhere on the interwebs! 

If we wipe out our cookies and log in again we can embed media, but just once.

Hoping someone has some insight as to the real meaning of this error considering that the JWT being POSTed is unique each time.

Thanks!