Excel may take an unusually long time to open a second workbook after the first one loads. This specific slowdown occurs in the Microsoft 365 Version 2402 update. A background process related to file validation gets stuck, causing the delay. This article explains the cause and provides a permanent fix for the issue.
Key Takeaways: Fixing the Second File Open Delay
- File > Options > Trust Center > Trust Center Settings: Disables the Protected View setting that triggers the slow validation process.
- Disable Protected View for files from the Internet: This specific setting is the primary cause of the slowdown in version 2402.
- Update to a newer version of Microsoft 365: Microsoft has released a fix in later updates, making an update the most reliable solution.
Why Version 2402 Causes a Slowdown on the Second File
The Microsoft 365 Version 2402 update introduced a change to how Excel validates files opened from potentially unsafe locations. A new security scan runs in the background when you open files. For the first file you open in an Excel session, this process typically completes quickly. However, a bug in this version causes the validation logic for the second file to enter a waiting state. It incorrectly checks for the completion of the first file’s scan, leading to a prolonged delay before the second workbook appears.
This problem is most noticeable when opening files downloaded from the internet or email attachments. These files are automatically flagged for inspection in Protected View. The slowdown does not usually affect files opened from trusted network locations or your local Documents folder. The issue is confined to the Version 2402 build and has been corrected by Microsoft in subsequent monthly updates.
Steps to Disable Protected View and Fix the Delay
The most direct workaround is to adjust the Protected View settings. This temporarily bypasses the faulty validation process. Remember that Protected View is a security feature, so only disable it if you trust the source of your files.
- Open Excel Trust Center Settings
With any workbook open, click File in the top-left corner. Select Options at the bottom of the menu. In the Excel Options window, choose Trust Center from the left sidebar. Then, click the Trust Center Settings button on the right. - Navigate to Protected View
In the Trust Center dialog box, select Protected View from the left-hand list. You will see several checkboxes that control when Protected View is enabled. - Disable the Key Setting
Uncheck the first option: Enable Protected View for files originating from the Internet. You may also uncheck the option for files located in potentially unsafe locations. Click OK to close the Trust Center, then click OK again to close Excel Options. - Restart Excel and Test
Close Excel completely and restart the application. Try opening two files that previously caused the slowdown. The second file should now open at normal speed.
Update Microsoft 365 to the Latest Version
The permanent fix is to update your Office installation. Microsoft has patched the bug in updates released after Version 2402.
- Open any Office application
Launch Excel, Word, or Outlook. - Check for updates
Click File > Account. Under the Product Information section, click the Update Options button. Select Update Now from the dropdown menu. - Complete the update
Office will download and install the latest updates. You must close all Office applications for the update to finish. Restart your computer after the process is complete to ensure the fix is fully applied.
If the Slowdown Persists After Applying the Fix
Excel is Still Slow Opening Local Files
If disabling Protected View did not help, the problem might be unrelated to the version 2402 bug. Check for other performance factors. Large files with complex formulas or many links can be slow to open. Try opening the file on a different computer to see if the delay is specific to your system. Also, ensure your computer has sufficient free RAM and that Excel is not running in compatibility mode.
Protected View Re-enables Itself After an Update
Major Office updates can sometimes reset security settings to their default values. If the slowdown returns after an update, you need to revisit the Trust Center. Follow the steps above to disable Protected View for internet files again. Your previous setting was overwritten by the update process.
Opening Files From a SharePoint or OneDrive Link is Slow
Files stored online may have additional latency. The delay might be from network speed, not the Excel bug. Try syncing the file locally with OneDrive and opening it from your synced folder instead of directly from the web link. This often improves open times significantly.
Workaround vs. Update: Key Differences
| Item | Disable Protected View (Workaround) | Update Microsoft 365 (Fix) |
|---|---|---|
| Primary action | Change a security setting in Excel | Install the latest Office update |
| Security impact | Reduces protection for files from the internet | Maintains all security features |
| Permanence | Temporary; may be reset by updates | Permanent resolution of the bug |
| Best for | Immediate relief before updating | Long-term stability and security |
| Admin rights required | No | Sometimes, for corporate installations |
You can now open multiple Excel files without waiting for the second one. The most reliable solution is to update your Microsoft 365 apps via File > Account > Update Options. If you need an immediate fix, adjusting the Protected View settings will stop the delay. For advanced users, checking the Windows Event Viewer for Office-related errors can provide more details if other problems occur.