I have seen this in the following situation, as it is not able to forward the Kerberos ticket:
- Edge with "InPrivate" Mode
- Edge with "Browse as Guest" Mode
Be careful about testing in Edge because of the following (Internet Explorer is better for SSO Testing, but not always available):
- Cached Credentials when Signed-In in Edge (edge://sync-internals/), https://learn.microsoft.com/en-us/deployedge/microsoft-edge-troubleshoot-enterprise-sync