Quick answer: Construct 3 game pinch gesture also firing during single-finger scroll? Touch object treats two-finger scroll as pinch - filter by touch count via Touch.TouchCount.
Phone player scrolls a list. Game registers a pinch-out and zooms the camera mid-scroll.
Gate by touch count
Pinch handler: System > Compare two values > Touch.TouchCount = 2. Single-touch scrolls don't trigger.
Or use the Pinch behavior
Construct 3's Pinch behavior handles this internally. Adopt over manual gesture code.
Test on real device
Browser touch emulation often fires multi-touch differently from hardware. The bug surfaces on phones, not in dev.
“Multi-touch gestures need touch-count gating. Single-touch is the same code path.”
List your supported gestures explicitly. Pinch, swipe, tap, long-press - each has a clear input contract. No contract = no bug surface.