Failing with Amazon SES

I am using WP Mail SMTP together with LearnDash + ProPanel + Uncanny LearnDash Groups. Test emails work fine as do the common transactional emails (add user, password reset, etc). However, when I send group email through ProPanel or Uncanny LearnDash Groups the message send fails.

The main difference between email that works and that doesn’t:
– Email that works is sent to one user at a time with the recipient in the TO field.
– Email that does not work is sent to a group of users at the same time. ProPanel leaves the TO field blank, Uncanny LearnDash Groups puts the sender email address in the TO and FROM field, and both then put the list of intended recipients in the BCC field.

I know that in the past Amazon SES had a limitations on email addressed to a list of BCC addresses without a TO address, but it is now supported and I can confirm that it does work using the very same SMTP user account to send test messages through my desktop email client.

Is this a known issue with WP Mail SMTP? How can I see diagnostic information about the failed sending attempts?