Hello,
Based on your test the authentication method must be "Defined on user record (legacy)". Unfortunatelly I cannot change the authentication from "Username and password" and I will explain why.
We have connected more than one domains with the firewall. In these domains there are same sam account names (eg test@domain1, test@domain2 etc). In this case with authentication method "Defined on user record (legacy)", when a vpn user enters credentials at the Mobile app, search takes place only in one domain.
However, I tested with authentication "Username and Password" and it works only if site is recreated. It this case "Standard" authentication method is disapperared. It is ok for my case.
Thank you very much for the assistance.