I have almost identical problem. Cannot save newsletter changes. I’m using v2.7.10. Main WordPress version recently updated (automatically) by my managed service to v4.8, for which MailPoet seems not to be tested. Could this be the cause of the problem?
Also experiencing difficulties getting daily automatic newsletter to send out emails, but I am a new user, and may need to be more persistent! But I wonder if this is a connected problem.
