Problem statement
When users navigate out of the app during an MFA challenge, like to open an Authenticator App to copy and paste the MFA code, the MFA challenge is terminated and throws a 401 error.
Cause
This is a limitation of Classic Universal Login due to a lack of control over this behavior, where there is a chance an IOS update has changed the behaviour of minimizing apps that require cross-origin polling. iOS is terminating the requests, not Auth0 services.
Solution
The recommended solution is to move to New Universal Login.