Login in "Development" doesn't work in "Live"


I have an app that has worked in production for some time. We recently migrated to a subdomain and things started breaking in the live version that are still working great in development

I’ve narrowed down the problem happening at login (by sending login page to an intermediate page to list username and login status)

It seems in “development” users are logging in no problem and able to access all user data, but in “live” users can pass the login page but the rest of functionality is as if they’re not logged in (i.e. can’t display “Current User’s Email”).

Any idea what this could be??