Added cause to SCIM error

doc/user/group/saml_sso/troubleshooting_scim.md

@@ -169,6 +169,7 @@ when the:
 
 - User exists, but does not have a SAML identity linked.
 - User exists, has a SAML identity, **and** has a SCIM identity that is set to `active: false`.
+- User exists, but is not a member of the associated top-level group and SAML SSO enforcement is enabled.
 
 ```plaintext
 The member's email address is not linked to a SAML account or has an inactive