Dear @kLonza,
Good day! Thank you for posting your question in the Microsoft Q&A forum.
We apologize for any inconvenience you may encounter when using our services/ products. Based on your description, kindly try these following steps:
To help you with your issue, we need more specific information from you:
Clear Cached Credentials
- Delete the account from the iPhone, restart the device, and reinstall the Outlook app. This clears any corrupted tokens or cached credentials
Check Conditional Access Logs
- As an admin, review the sign-in logs in Microsoft Entra to see if any Conditional Access policies are being applied unexpectedly.
Here is a reference: Configure adaptive session lifetime policies - Microsoft Entra ID | Microsoft Learn
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