please note that the aggregated grades are kept inside the Workshop only until you finish the Grading evaluation phase and close the workshop. Grades are written into the course gradebook when and only when the workshop is being closed (i.e. the phase is being changed to "Closed").
It is expected that the teacher uses the grading evaluation phase iteratively until their happy with the result. And that is why students do not have access to their grades until the workshop is closed.
Also note, to use the "late submissions" feature, you do not actually need to switch the workshop back to the submission phase.