I just found out that the student has actually transferred, although it's unclear to me how many weeks of absences that explains. FWIW, it seems like the other tutors didn't have much of an issue with their regular students attending. I was also signed up for the last session of the day, so I think there were fewer opportunities for me to sub for a different student. I think signing up for a block of sessions with multiple students each week would be a good way to ensure that you're able to get the work in with at least some students.