Ok this is weird:
I was on Computer Science Meta. I wanted to make an account. So I clicked “sign up”, taking me to http://cs.meta.stackexchange.com/users/signup?ssrc=site_switcher&returnurl=https%3a%2f%2fcs.meta.stackexchange.com%2fusers%2fopenidconfirm
Clicking on “Confirm new account” took me to https://cs.meta.stackexchange.com/users/openidconfirm, which has an error message. No account was created.
Definitely something is wrong...
On responsive, the button redirects to main and it works.
This doesn’t happen on main Computer Science.
Safari iOS 12.4.1, iPhone 7. Mobile site (not responsive). I don’t use Facebook/Google to sign up.