New subscribers sent to admin login; welcome communication not sent

I’ve had two people contact me today (and I confirmed this activity by signing in as a test user) to say they received an email with a link to login to as an admin. They see a stripped down version of the WP site, (basically the ‘edit profile’ area) including my notices to upgrade certain plugins etc. This is NOT COOL.

Also, the confirmation email (set up in Communications, set to send 0 days after sign up) is not going out.

Any ideas here?

I am using the latest versions of wordpress and membership.