I can't see through why it works but there seems to be a solution to the issue of using two Windows PCs in parallel to develop iOS apps for one iPhone:
On the first PC you create a mobile app with Visual Studio. Xamarin Setup Hot Restart works without any problems. You can build, deploy and launch your app.
However when you switch your work to the second PC and create another mobile app with Visual Studio things become more complicated. After having performed Xamarin Hot Restart, you have to go to the property page of iOS Bundle Signing and switch to Manual Provisioning and without doing anything more back to Automatic Provisioning and Select Team. After this detour you can build, deploy and launch your app.
When you switch your work back to the first PC you have to apply the detour again.