Cognito MFA user initialization redirects to white page

Question

I have configured an app client with appropriate redirects. Login and Log Out flows work. The only broken flow is initial sign in - the first time a user goes to the page (I have self sign up deactivated), they are correctly prompted to change their password. Then an MFA screen pops up with the QR code. Upon successfully entering your code, user is redirected to a blank page.

If one were to dig in with BURP or Chrome tools, you'd find that upon completion of MFA registration and return to the page, API calls are happening, but the DOM doesn't draw anything.

One thing I have noticed is that only on MFA set up response, the user is routed to 'https://sub.my.domain' instead of what I would expect (and what is set up in the app client/hosted UI) which is 'https://sub.my.domain/' (the final forward slash is missing).

Could this be the culprit, and if so, how to I get MFA successful set up to route to a specific URI? I can't find a place to specify URI other than the app integration tab.

Answer

I get to answer this one myself, but here it is if anyone else runs into it:

It looks like on the MFA set-up flow ONLY, upon successful entry of the Google Authenticator code, for one hot second the "user" that you can get from useAuthenticator is empty, causing an error in my conditional statements, manifesting as a white screen on the build version.

Cognito MFA user initialization redirects to white page

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