I have reviewed the troubleshooting closed thread at https://sendy.co/forum/discussion/237/emails-not-sending-to-subscribers-on-different-lists-in-different-brands/p1
which appears to be the same issue that I am having. I have sent out 2 campaigns to 2 different lists (1 list per campaign) and there is a large discrepancy between the number of active users and the number or emails that have been sent. See my stats below:
-> campaign 1 -> list size 8558 contacts -> sent to 7257 contacts -> 15% of contacts did not receive email
-> campaign 2 -> list size 3903 contacts -> sent to 1414 contacts -> 64% of contacts did not receive email
There is no consistency between these 2 results so it's hard to find a causal link. Sendy was obviously able to send to 7257 contacts for campaign 1, so it shouldn't have had any issue with campaign 2 with a list size of 3903. And the system is reporting that the campaigns were sent successfully even though they weren't.