We have enhanced the IMAP certificate checks so this is an expected result when your certificate name does not match the hostname. Please either use the correct certificate or match the server address found in your account settings (Menu > Accounts > the relevant account - IMAP tab - Host) with the one in the current certificate details.

If you are redirected on the server and the names can’t match, you can also choose the possibility to connect with the current settings and remember this choice.