I created a test prototype with only 2 screens. None of the screens are linked.
When I view them on my iPhone in any browser or the Figma app, if I tap the right side of Screen 1, it jumps to Screen 2. On Screen 2, if I tap anywhere on the left side, it jumps to Screen 1.
This is clearly a bug.
However, I found a work around. If I add a “Flow starting point” to any of the screens, the problem goes away.