Run on iOS Device fails

I'm getting errors if trying to run on iOS Device

sometimes:

Error parsing JSON at 1:1: illegal value/Applications/daten/...5.15/ios/mkspecs/features/qtprf
Failed to parse qmlimportscanner output.

and sometime:

Project Error: Could not resolve SDK Path for 'iphoneos' using --show-sdk-path Error while parsing file /Applications/...my.pro. Giving up.

I can build the project successfully and run from XCode.

From QtC I also can run on iOS Simulator.

While playing around I found a reproducable scenario:

If I quit QtC while iOS (Device) is current platform and restart QtC, then it fails.

If I switch to iOS Simulator, then quit QtC, reopen QtC and then switch from iOS Simulator to iOS (Device) all works as expected.

Is reproducable for me - so as a workaround I'm always switching to iOS Simulator before quit QtC or switch to another project.