Originally mentioned in MDL-78916. Since that issue changes the mod_form for mod_lti instances such that there isn't a 'tool type' selector any more, it's possible that tool instances can now be stale. If the teacher were to delete the course tool that the instance references, there is no way to fix this, and the instance must be deleted/recreated.

We already throw an exception when launching stale tool instances; this issue is about doing something similar on the "Edit settings" page of the activity.