Using latest WP installation version, when I try to initially connect the plugin to my Mailchimp account using the Connect button in the WP installation, I'm getting the same 500 error others are noting.
I've asked WP Engine, my host to whitelist your IPs & the domain you listed in earlier posts here. I've also deactivated all plugins & cleared my cache. The 500 error is still happening.
This is greatly frustrating and renders Mailchimp almost unusable. You can't want this problem, yet I see it's so common in the WP threads.