The account creation happens with the [s2Member-Pro-Stripe-Form] shortcode. This works exactly as it is supposed to. When a user signs up, their account is created and the "success" variable works like it's supposed to, sending them to the correct URL after they sign up.
So everything works exactly as it's supposed to except that they are not logged in.
Have you worked with Auto-login before and have it working? My understanding is that by placing the code in the mu-plugins folder, the user is just supposed to be logged in after they sign up. Is that correct?
So basically, if S2Member has been working on my site for over a year and now all I want to change is make it so new users are logged in automatically after signing up, I just need to follow the directions ((https://s2member.com/kb-article/auto-login-on-registration/) and that should be all I have to do, correct?
This is what I did and they are not being logged in automatically.