new members automatically being unsubscribed (not joining mailchimp list)

this is either a mailchimp problem or membership 2 pro

new members who sign up are not joining the mail list for a newsletter via mailchimp

they don't receive an email but I (as admin for the site) receive an email saying they have unsubscribed from the list. we are testing the memberships so colleagues are joining and I know they have not unsubscribed or opted out

can you assist? I have extended support access to the site