Has this issue been solved? I encountered the same issue! This is a blocker for me to continue using this newsletter plugin.
My symptom is that if I go to Diagnostic from the newsletter Settings and send the test email, it works. But if I go to Status and send a test message, it failed with “Last test failed with error “SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting”. “