If the issue persists, repeat the process and choose Online Repair. This process replaces damaged core files without removing your data or customizations. 21Vianet also expect customer to collaborate at reasonable level accordingly.

⃣ Reset Browser Cookies & Cache

If your admin enabled Modern Authentication (MFA), try disabling it temporarily via Azure Active Directory → Properties. Alternatively, generate an app-specific password if using Outlook 2016 or older. This resets your authentication cache and forces a fresh token request.

Microsoft 365 Apps Crashing After Update — Step-by-Step Repair Guide

• The steps to access the repair tool vary depending on your operating system.
• It automatically diagnoses and repairs many Office 365 problems — including search indexing and sync issues.
• The Microsoft 365 Copilot app brings together your favorite FixTechGuide Office 365 support apps and Copilot in one intuitive platform.
• If your admin enabled Modern Authentication (MFA), try disabling it temporarily via Azure Active Directory → Properties.
• Microsoft 365 crashes after updates can be frustrating, but these fixes will restore stability quickly.
• For more self-help resources, see Microsoft 365 operated by 21Vianet.

For iPhone users, reinstalling Outlook or updating to the latest iOS often resolves stuck sign-in loops instantly. Many users have both personal Microsoft accounts (e.g., FixTechGuide Office 365 troubleshooting Outlook.com) and work/school Office 365 accounts. If both are signed in simultaneously, the system can confuse the authentication path.

? Fix Office 365 Login Issues on Mobile

21Vianet assigns a severity level to a case when it’s opened, based on an assessment of the issue type and customer impact. Examples of issue types and severity levels are shown in the following table. Authorized administrators can use the Microsoft 365 operated Office 365 Sync Errors Fix by 21Vianet portal to submit service requests online and access support telephone numbers.

Step 2 – Update Outlook and Office 365

Go to Settings → Windows Update and install all pending updates. Then open any Office app → File → Account → Update Options → Update Now to ensure both are synchronized. Go Fix Outlook and Office 365 Errors 2025 to Control Panel → Programs and Features, select Microsoft 365, and click Change → Quick Repair.





Microsoft 365 with Microsoft Teams helps deliver a complete, secure solution to help everyone work better, smarter, and more cohesively. Microsoft Create has professionally designed, fully customizable templates to help you get things done. Find solutions to common problems or get help from a support agent.