@holathebeach
Well it seems that you have flow filter “Has placed order zero times since starting this flow” and the flow filters are checked before every email is sent out. So when the first email was sent they didn’t had an order but then I assume they placed an order before first and second email and when the time got to get the 2nd email they were skipped because they were not meeting the condition anymore.
This is usual filter for welcome flow so you should expect people are removed from the welcome flow after they buy. If you don’t want that you can remove that filter but it is not recommended since welcome is usually pre-purchase flow.
Btw as Flowium have a lot of resources on our website and here is one on “How to Create a Perfect Welcome Email Series for eCommerce”