Updates from DoIT – the problem is still ongoing, but possible workaround and possible fix for web client:
UPDATE, 2/24/21, 2:00 PM – Technologists continue to work on resolving this issue. In the meantime, you can follow steps outlined below as a workaround: https://kb.wisc.edu/office365/39838 (“Access the service account via ‘Open Mailbox’ feature in Outlook on the web (browser)” section).
UPDATE 2/25/2021, 8AM – For some users, clearing browser cache and cookies (for all-time), has resolved the issue – https://kb.wisc.edu/12384.
Read the full article at: https://outages.doit.wisc.edu/outage/946dba494c5719a4db0bd943d5be4a17e83a8566a9