Hi Daniel,
Thanks for your feedback and I understand the inconvenience.
I understand that you have tried many ways to set the Office 365 account in your mobile device. To narrow down the root cause of the issue, if it is possible, please add this Office 365 account in another mobile device to check if the issue will persist. Or please add a non-Office 365 account (such as Hotmail) in your mobile.
Moreover, could you please try using m.outlook.com as the server name to check if there is any improvement? You efforts are appreciated.
Best Regards,
Anna Shi