The same issue. The test emails are sent, but the newsletter sending is not working. I run the wp-cron.php manually many times but it does not solve the problem.
As I read this is common problem and the plugin is absolutely unusable now so please handle this on high priority.
Here is the diagnostic information (Scheduler execution interval is so strange):
WordPress Cron System ENABLED. (it’s ok)
WordPress schedules newsletter – 300 s
newsletter_weekly – 604800 s
hourly – 3600 s
twicedaily – 43200 s
daily – 86400 s
Delivery Engine It seems the cron system is not working. Reload the page to see if this message change. Trigger now
If inactive or always in “running now” status your blog has a problem: read more here.
Collected samples 300
Samples are collected in a maximum number of 300
Scheduler execution interval mean 3738 seconds (KO)
Should be less than 300 seconds. Read more.