There is no need for MITM nor for installing certificates on clients when you explicitly set the proxy on clients. Squid will use CONNECT for HTTPS on sslports ACL to connect to HTTPS websites. If you want MITM, make the proxy transparent and stop configuring it on clients.
I want to be able to see HTTPS traffic for both inspection + caching. I've tried not configuring the proxy on clients and leaving on transparent mode. That's throwing errors too. Am I the only one having this issue?? I'm guessing the DNS alternative name isn't being mimicked by Squid properly. Since on Chrome mobile, that's an error it's saying "DNS alternative name invalid".