Azure AD B2C Custom Policy - Throwing UserMessageIfServerError: An exception has occurred.

Hi Team,

We have started implementing Azure AD B2C custom policy for SignUp/SignIn.
On execution of custom policy, Signup/Signin screen is shown .

On Signup screen, we do the verification then we enter the details like password and name and continue to MFA.

This MFS screen throws error "Sorry, but we're having trouble signing you in"
and exception it shows is "UserMessageIfServerError: An exception has occurred."
I am attaching the screenshot of error as well

Let me know if anybody has faced this issue and know the cause and possible solution for the same