SharePoint links stop working for external Users

Since you've already checked the basic settings and even Microsoft Support hasn't found a solution, this points to a more complex problem involving permissions, security policies, or backend SharePoint behaviors.

In this response, I'll walk you through several possible causes and their respective solutions, including sharing policies, conditional access settings, session expirations, and permission conflicts. By methodically testing these factors, you should be able to pinpoint what's causing the intermittent access issues and find a way to resolve them.

Possible Causes & Solutions

1. SharePoint Sharing Policies & Expiration Settings
🔹 Check Org-wide Sharing Settings:
Even if links are set without expiration, tenant-level or SharePoint settings might enforce stricter rules.
➡️ Verify in Microsoft 365 Admin Center:

Go to Microsoft 365 Admin Center → Settings → Org Settings → Security & Privacy → Sharing.
Ensure the external sharing level is set to "Anyone with the link" or "New and existing guests" if that's the intended behavior.
➡️ Verify in SharePoint Admin Center:

Navigate to SharePoint Admin Center → Policies → Sharing.
Check if external sharing is restricted after a certain period.
Under Advanced settings for Anyone links, verify if there is an expiration setting.

2. Conditional Access / Security Defaults / MFA Expiry
🔹 Check Conditional Access Policies
If your organization has Microsoft Entra ID (formerly Azure AD) Conditional Access policies, they may be revoking access after 24 hours due to session expiration or MFA enforcement.

➡️ Test with a different external user who has not been added before to see if the issue persists.

➡️ Check in Entra Admin Center:

Go to Microsoft Entra ID Admin Center → Security → Conditional Access.
Look for policies that might apply to external users (like "Require reauthentication after X hours").
🔹 Session Expiry for External Users
Some security settings might log out external users after a day. If so, they may need to re-authenticate, which could explain the intermittent access issues.

➡️ Try asking an affected user to sign out and back into their Microsoft or guest account.

3. External User Licensing Issues
If your external users access files through SharePoint's B2B (guest user) model, there could be licensing issues. If your organization has moved to Microsoft Entra External ID, licensing requirements have changed.

➡️ Check if these external users are "Guest Users" or "External Members" in Microsoft Entra Admin Center. If they require a paid SharePoint license for extended access, their access could be revoked intermittently.

4. Link Behavior & Permission Conflicts
🔹 Check if Sharing is Affected by Link Type

"Anyone with the link" might be disabled after a time due to policy enforcement.
"Specific people" links could be revoked if the guest’s email address doesn't match their Microsoft account login.
➡️ Test switching from "Anyone with the link" to "Specific people" and vice versa.

🔹 Check for Link Conflicts

If multiple team members share links differently (e.g., one shares an "Anyone" link, another shares a "Specific people" link), previous permissions may get overwritten.
➡️ Have the external user try accessing the document directly via
https://[YourTenant].sharepoint.com/sites/[YourSite]/Shared Documents/[FileName]
(instead of the shared link).

5. SharePoint Indexing & Caching Issues
🔹 Delays in Permission Propagation
If SharePoint takes too long to update permissions, links may appear to "stop working" until the indexing catches up.

➡️ Try manually re-syncing permissions:

Open the document in SharePoint Online.
Go to Manage Access.
Remove and re-add the external user.
Have them sign out and back into their Microsoft account.
🔹 Check if Access is Revoked in Audit Logs
➡️ Go to Microsoft Purview (Compliance Center) → Audit Log Search and filter for "File Access Denied" events to see if the system is revoking access.

Next Steps
✔ Test links with different external users (to isolate whether it's user-specific).
✔ Check Conditional Access settings for session expiration policies.
✔ Try different link types ("Anyone" vs. "Specific People").
✔ Manually refresh permissions and have the external user re-authenticate.
✔ Monitor Audit Logs to see if SharePoint revokes access automatically.