Receiving a blank page after logging in, course already in session

I have one course where none of the students or the instructor are able to proceed past the login. They receive a blank page. I, as an admin, am able to view their course perfectly. I even tried enrolling as a student, and had no problems. Students have been active in the class for a week now, without problems. The issue seems to have started on the weekend.

Please help, thank you,
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