AutoSSL uses different domain SSL for all newly created add-on domains

When I setup a add-on domain for example domain1.com, AutoSSL uses a HTTPS certificate from a different domain thats on the account (domain2.com) or sometimes it uses the theirsubdomain.mydomain.com. My client thought that he was hacked by my other client site domain2.com when he checked and saw that he was using the HTTPS certificate. How would I prevent AutoSSL from doing that and just using domain name for the add-on for the certificate?