Hey all,

we’re troubleshooting an issue that started ~2–3 weeks ago across our org and I’m trying to connect a few dots. Would appreciate any confirmation / workarounds.

🧾 Environment

• Office: Microsoft Office Home & Business 2021
• Apps: Outlook Desktop, Excel Desktop
• Source: SharePoint / OneDrive links (.xlsx)
• Auth: ADFS (on-prem)
• OS: Windows 10/11

🔴 Main issue

When clicking a SharePoint Excel link from Outlook Desktop:

• Outlook forces opening in Excel Desktop
• Excel opens → blank (white) workbook
• No error, no content

✅ Expected behavior

• Link opens in browser (Edge/Chrome)
• File loads correctly in SharePoint / Excel Online

🧪 Key observation (VERY important)

If we strip query parameters from the URL, it works:

❌ Broken:

https://tenant.sharepoint.com/.../file.xlsx?d=xxx&e=xxx&sharingv2=true&fromShare=true&at=9

✅ Working:

https://tenant.sharepoint.com/.../file.xlsx

🔎 What Outlook seems to do

Outlook Desktop appears to convert the link into something like:

ms-excel:ofe|u|https://...

or directly invokes:

excel.exe "https://..."

Which forces Excel Desktop instead of browser.

🧠 Hypothesis

This looks like a mix of:

1. Excel not handling query params correctly
2. Auth (ADFS) breaking inside Excel embedded WebView
3. Outlook forcing desktop handler instead of browser

🔍 What we found (Process Monitor)

From ProcMon:

• Excel accesses:%localappdata%\Microsoft\Office\16.0\Wef %localappdata%\Microsoft\Office\16.0\OfficeFileCache %localappdata%\Microsoft\OneAuth %localappdata%\Microsoft\IdentityCache
• Heavy activity around:
  • WebView / embedded browser components
  • identity/token cache
  • SharePoint URL parsing

👉 Looks like Excel is trying to:

• authenticate via embedded WebView
• resolve the SharePoint URL with params
• failing silently → resulting in blank screen

🧹 What we tested

Clearing caches:

%localappdata%\Microsoft\Office\16.0\OfficeFileCache
%localappdata%\Microsoft\Office\16.0\Wef
%localappdata%\Microsoft\OneAuth
%localappdata%\Microsoft\IdentityCache

👉 Result:

• temporarily improved behavior
• links sometimes started opening in browser

Re-registering Excel:

excel.exe /unregserver
excel.exe /regserver

👉 Result:

• reset protocol handler
• Excel launched “first-run”
• behavior changed temporarily, then reverted

SharePoint setting:

Library → Advanced Settings → Opening Documents

• set to:
  • “Use server default (open in browser)”
  • also tested “Open in browser”

👉 Outlook still forces Excel Desktop

Security finding

We also hit:

>

👉 SharePoint was being treated as:

• Restricted Sites (zone issue / GPO?)

📱 Related issue (maybe same root cause?)

On mobile:

• Microsoft Teams / Microsoft Outlook
• login → white screen during auth
• tied to ADFS

👉 suggests:
WebView + ADFS compatibility issue across platforms

❓ Questions

1. Has anyone seen Excel Desktop fail specifically on SharePoint URLs with query params?
2. Is Outlook Desktop known to incorrectly force ms-excel: handler in Office 2021?
3. Any way to force browser-first behavior (without O365 policy)?
4. Could this be a regression in:
   • Excel WebView handling
   • ADFS auth flow
5. Any registry/GPO workaround for Office 2021?

💡 Current theory

This is NOT just one issue, but a combo of:

• Outlook link handling (forcing Excel)
• Excel WebView rendering/auth
• ADFS compatibility
• URL query param handling
• possibly recent update/regression

Any insights, confirmations, or workarounds would be hugely appreciated 🙏