OneNote for iPhone repeatedly returns to Sign In after successful Microsoft 365 Business authentication

I am having this exact issue, none of the troubleshooting above has worked. It's specifically linked to OneNote because all other apps can be signed into upon reinstall.

Hi,

Thank you for your detailed troubleshooting and for clearly documenting the behavior across your devices and Microsoft 365 services.

Based on the evidence you've provided, you've already narrowed the issue down significantly. Because the same Microsoft 365 Business account works successfully with Teams, OneDrive, Microsoft 365 on the web, OneNote for the web, and OneNote for Windows, this appears more likely to be related to how the OneNote iOS app is establishing its authenticated session rather than an issue with the account itself, OneDrive, licensing, or notebook synchronization.

Please try the following additional troubleshooting steps:

1/ Perform a full OneNote reset

Since you've already reset login credentials, the next step is to perform a more complete OneNote reset:

Confirm that your notebook is accessible in OneNote for the web (which you've already verified).

Force-close the OneNote app.

On your iPhone, go to Settings > OneNote > Reset OneNote.

Enable both:

• Delete All Notebooks
• Delete Login Credentials

Reopen OneNote and sign in using only your new Microsoft 365 Business account.

This ensures that any potentially corrupted local notebook data or cached authentication information is removed before a fresh sign-in attempt.

For reference: Reset Microsoft OneNote between users on a shared iPad or iPhone | Microsoft Support

2/ Update All Microsoft 365 Apps

Microsoft has documented issues on iOS/iPadOS where Microsoft 365 applications may repeatedly prompt for sign-in or fail during the account initialization process. In some cases, these issues were related to a timing condition during app startup that affected the post-authentication process.

Even if your new tenant is not managed through Intune, your symptoms closely resemble a situation where authentication succeeds but the application fails to establish the authenticated session.

Please update the following apps from the App Store:

• OneNote
• Microsoft Authenticator
• OneDrive
• Teams
• Outlook
• Word
• Excel
• PowerPoint

After updating, restart the iPhone and test OneNote again.

For additional information, please see: Unexpected sign-outs in Microsoft 365 iOS apps with Intune MAM | Microsoft Support

3/ Remove the old employer account from the shared Microsoft identity surface, if possible without re-enrolling

Although the sign-in loop occurs even when you select only the new Business account, the presence of the old employer account may still be relevant because Microsoft applications on iOS can share authentication state through Microsoft Authenticator and other Microsoft identity components.

Microsoft's guidance for Microsoft Entra ID applications notes that iOS single sign-on relies on brokered authentication and shared token storage. If stale account information or authentication artifacts remain, they can occasionally interfere with application sign-in experiences.

For reference: Why does an MSAL-based iOS app keep asking for credentials with Microsoft Entra?

If the former employer account appears to be only a stale account entry, you may want to remove it from Microsoft Authenticator and other Microsoft applications where possible. However, do not proceed with any enrollment or security-registration prompts from your former employer's organization if you do not wish to reconnect your personal device to their management policies.

If the issue persists:

If OneNote continues to return to the Sign In screen after successful authentication, the next step would be to open a support case with Microsoft. Because the account and notebook function correctly everywhere except the OneNote iOS app, Microsoft support can review sign-in and service logs that are not visible from the client side.

You can create a support request through the Microsoft 365 Admin Center by following this guide: Get support - Microsoft 365 admin | Microsoft Learn .  

I hope this helps move the investigation forward. Please let me know the results of the full reset and whether removing the old account entry changes the behavior. I’d be happy to assist. 

Thank you for your patience and understanding.

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