Why am I seeing customers who purchased in the waiting queue to receive the Abandoned Cart flow?
The way this flow works, everyone who is captured by the initial trigger - Checkout Started - will queue up for the first email in the flow and appear under "Waiting." At a person's scheduled send time, Klaviyo will check the flow's filter - "Has Placed Order zero times since starting this flow" - and skip anyone who completed a purchase. If you explore the Recipient Activity tab for a given email in your flow, you can see the number of total recipients. If you click on the 'Skipped' dropdown, you will see the number of individuals falling into the "Skipped: Fails Flow Filters" bucket. These are the people that entered your flow when they started a checkout but were then skipped because they purchased before the email was set to send.