Mosaico 2.0, Drupal 7.64 - "Sorry an error occurred and your information was not saved"
Have you tried asking your web host to see if you're throwing out a server based error, like a ModSecurity issue? I regularly run into those with CiviCRM when I'm doing emails and have to get the server techs to whitelist a process for me so that it doesn't give me an error. Other than a piece of bad formed code (like when someone has copied something from Word or whatever), it's always been this kind of issue for me.