Sign-in & Login Problems

How to Fix Office 365 Sign-In Screen Flashing on Mac

Maira Mehtab Sep 20, 2026 869 views

Question details

The user needs to resolve an issue where the Microsoft 365 sign-in screen loops, flashes, or resets continuously on a Mac.

Product: Microsoft Office 365
Device & OS: macOS
Scenario: Attempting to sign in to Office 365 applications on a Mac, particularly after installing third-party security software.
Observed behavior: The sign-in window repeatedly flashes and resets automatically, preventing the user from entering credentials or authenticating the account.

Before you start

Ensure you have your Microsoft 365 account credentials handy and check your internet connection before proceeding. You should also save any open files in other applications in case a system restart or user profile switch is required.

Solution 1Recommended

Troubleshoot Security Software Conflicts

Identify if third-party antivirus tools like Malwarebytes are blocking the Office 365 authentication processes.

Security software can sometimes mistakenly intercept or block the network requests required for Microsoft's authentication windows, causing the screen to flash or reload continuously.

Open security software

Launch Malwarebytes or any other active antivirus application currently running on your Mac.

Disable protection temporarily

Navigate to the security settings and temporarily disable the real-time protection or web protection features.

Test Office sign-in

Launch Microsoft Word or Excel and attempt to sign in again. If successful, you can re-enable your antivirus and add Microsoft Office to its allowlist or exclusion list.

Solution 2

Verify Account and Subscription Online

Ensure your Microsoft 365 account is active and accessible via the web portal to rule out account-level issues.

Solution 3

Create a New macOS User Profile

Test for corrupted user profile settings or keychain issues that might be interfering with the Office login window.

Free Microsoft Office alternative

Try WPS Office for a Stable Mac Experience

If Microsoft Office 365 continues to experience login loops or conflicts on your Mac, consider switching to WPS Office. It provides a lightweight, highly compatible, and free alternative that does not rely on complex background authentication services to edit your files.

1. Download WPS Office: Visit the official WPS Office website and download the Mac version installer.
2. Install the application: Open the downloaded .dmg file and drag the WPS Office icon to your Applications folder.
3. Open your documents: Launch WPS Office and instantly open your existing Microsoft Office files without complex sign-in setups.

Fully compatible with Microsoft Word, Excel, and PowerPoint formats (.docx, .xlsx, .pptx).Lightweight installation that avoids heavy background processes and login screen loops.Seamless transition with a familiar user interface designed natively for Mac.Free to use without mandatory subscription barriers for core editing features.

Frequently Asked Questions

Why does the Office 365 sign-in screen keep flashing on Mac?

This typically happens due to network connection conflicts with third-party security software like Malwarebytes, corrupted macOS keychain access entries, or temporary configuration glitches in your specific Mac user profile.

Does reinstalling Office 365 fix the login loop?

Reinstalling the software might not resolve the issue if the root cause is a blocked network connection from your antivirus or a corrupted local Mac user profile. It is best to test disabling your security software or trying a different user profile first.

How do I clear the Office credential cache on a Mac?

You can clear your cached credentials by opening the 'Keychain Access' app (found in Applications > Utilities), searching for 'Microsoft Office' or 'ADAL', and deleting those specific credential entries before restarting your Mac and trying to sign in again.

Can I use Microsoft Office apps offline if I cannot sign in?

If you cannot sign in to verify your Microsoft 365 subscription status, the desktop applications will eventually switch to reduced functionality mode. This will prevent you from editing, saving, or creating new documents until the login issue is resolved.

Login & Account Issues