If you experience the below warning message when selecting the calendar tile within MyDay then read through this article.
...
To find this you will need to go to Control Panel > Connectors > Exchange > Edit > Tick Use OAuth Authentication for Office 365.
...
Steps to resolve:
ONLY TO BE ACTIONED IF ALL STUDENTS ARE AFFECTED
One way to resolve this issue is by re-consenting on the myday office 365 app itself on Azure.
...