Thanks for posting this in the global Canvas Community. I am sorry you are seeing that error message.
It looks like this might have been happening in Speedgrader or the gradebook?
This can sometimes happen with large courses. In which case, a filter might need to be applied or disabled in the gradebook.
I have seen this happen sometimes when a setting for Launch SpeedGrader Filtered by Student Group is enabled in the course and a selected student is not in a group. It can easily be turned off and tested if that is the case.
If you haven't already, you could contact support to see if they can take a look at your specific example. I know I am late to this post, so you might have already resolved this.