'Assignment is no longer associated' on LTI submit of ContentItemSelection

[re...@el-tramo.be]

Hi,

I added a new LTI app to the Canvas demo environment, and used ContentItemSelection on this app to add an LTI link to an assignment. 

When this link submits back a grade using LTI outcomes, I get the following error:

     Assignment is no longer associated with this tool [EID_1509630000000543858]

The submitted sourcedId matches the one I got, and I haven't done anything to the app registration in the meantime. 

Does this have something to do with the fact that the LTI link is the result of a content-item-select, and the URLs don't map, or am I doing something else wrong?

thanks,

Remko