In your smart campaign screenshot "Status.PNG", it shows that the flow says to -- Do Nothing --
What this tells me is that no emails were sent. Basically the 537 leads all ran through that campaign and did nothing.
If you want to know what was changed in the smart campaign, for example, if it was indeed the flow that was changed, you'll need to contact support.
That's probably what happened - I was thinking that when the other admin went back and changed it on 3/21, they deleted the email that was previously selected. So there's a possibility it just never ran. Thanks!