Membership emails not going out consistently

We have 365 daily emails scheduled with out membership site, 1 going out per day, starting on day 1. They don't seem to be going out consistently. One member will get 5 emails in order then a few days will skip, another member gets the 1st email, then nothing for a few days. When they do come though they are sending on the correct days. How can we troubleshoot this feature?