The process was very drawn out and I got the impression Klaviyo was just stringing me along at some point. I had 6 interviews, including one take-home exercise after the last round which they said would take 8 hours to complete (but implied that I should take time to make it absolutely perfect to show them that I would be a good employee), but ultimately was rejected with one sentence of feedback. Meanwhile, in earlier rounds the technical aspects were almost trivial (simulate dice throws with python). There is no clear idea of what "they" want and why they reject certain candidates.