The primary view controller is wider than what is visible on screen to provide extra content when over-scrolling during a swipe action. It is 420 points wide, but 320 points is visible. So content that is aligned with the leading edge instead of the leading margin (or safe area, as you noted), will be partially off-screen. These two tweets show what I mean https://twitter.com/geoffhackworth/status/1283802290613354498

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