It looks like it has something to do with the relation between email and first name (you'll see that the initial/name in the email and first name are the same). This is causing some kind of bug. When we change the field to something unrelated, there is no problem in the execution.
I found a workaround by adding a dummy First Name field after the initial First Name field. Prepend it with underscores so it won't show up in your data: