Did you get any less radical workaround, I am also facing the same issue, rebooting MAC helps but is not consistent. Thanks

This works for me: Reason: Either the App store or something tool is downloading the app with the same identifier at the time Xcode is trying to launch the app on the Simulator or on MAC. Solution: Need to stop/delete all the running installs of the app with the same identifier. (How to stop -> that can be figured out to see either App Store/another tool) Then try again to launch the app with Xcode, this time it succeeds. No need to Reboot the simulator/Mac or reinstall Xcode. Thanks.

I have the same issue, Any solution found?