I upgraded to OS X 10.11.5 and Xcode 7.3.1 a few days ago and all seemed well. Then today after adding my new iPhone 6s Plus to the device IDs in my developer account and having Xcode do an automatic 'fix issue' to update the provisioning profile when trying to run my apps on my new device, I am now getting Invalid Device State errors on all my simulators in all my apps. Running the apps on my new device works fine, but all the simulators give me the error. I tried the solutions found here iOS Simulator: Invalid device state and here Invalid Device State - Xcode/iOS Simulator error but neither have resolved my issue. When I run xcrun simctl list all the devices show a status of Shutdown, which I assume is what the status should be. I then run xcrun simctl erase all and I get no errors. I then did a clean build and a clean build folder, and restarted my Mac, and still the error occurs after doing all these steps. This is really frustrating, and I hope someone can point me in the right direction. I always get nervous when it comes to upgrading OS X and/or Xcode because more often than not something breaks in my apps, or something like this occurs.
I tried everything possible to get this to work for two days. Finally I re-installed Xcode and that did it. In case someone runs into this issue and the regular solutions do not work, don't waste your time trying to figure it out, just re-install Xcode and save yourself some time.