Unable to open debug menu on ios 13.0

Hi, I’m profiling my game on ios 13.0 device (iphone 11), but I can’t open debug menu by 4 fingers tappping. So I add printf for NumActiveTouches in HandleTouchLoc of “IOSView.cpp”. But it’s so wired that xcode prints negative integer as I tap with multiple fingers. It prints -7 when I tap with 5 fingers. Is that an engine bug?

My envs:
macOS 10.15
Unreal 4.23.1
Xcode 11
iPhone 11 with iOS 13.0