Xcode 9 error: "iPhone has denied the launch request"
It may be code sign issue. Make sure you're signing with developer, not distribution.
It happens using Xcode 9.x or newer.
I tracked this problem down to the "debug executable" checkbox in the product scheme (product->scheme->edit scheme->info->debug executable checkbox). I unchecked that and this stopped happening (as well as a couple other weird issues - no output in console being one).
I have a workaround:
If you change the scheme to 'Ask on Launch' it works.
In Xcode top bar
Product > Scheme > Edit Scheme > 'Info' tab > Executable: "Ask on Launch"It's slightly annoying but it works.