I had two system design interviews, one with a staff engineer primarily focused on the back-end, and one with a senior engineer, more full-stack focused. (though they said it would be front-end, we spent more than an average amount of time time data modeling) Both interviews went well on my end. The backend interview I was immediately pressed forward to the next round. I did not "pass" the front-end round, which I was surprised about. I handled edge cases and even suggested product features. I also validated my assumption with a third unbiased party who suggested I would be moved forward as an L4/L5.