I have taken over teaching an open enrollment course which never concludes. I have to conclude all students manually. There are a lot of graduates (some from over a year ago) still on the roster. Yesterday I concluded 10 students. Today 8 of those students are back on my roster. This is the menu where I choose "User Details" and then I will choose "conclude".
How can I conclude students so they stay concluded?
It sounds like this is being caused by the sync between your SIS and Canvas. If your Canvas administrators are running automatic nightly syncs with the SIS, and the enrollments have not been concluded in the SIS, it would make sense that you would see the students reappear in your Canvas course each morning, despite having manually removed them.
I would suggest reaching out to your Canvas and/or SIS administrator at your institution, give them the names (and/or ID #s) of the student enrollments in question, and ask them to check on the status of these students in the SIS.