Watchkit compiles but won't run in iOS Simulator

I can compile and "run" (as evidenced by output in the console) my WatchKit Extension/App, but the Watch simulator window won't open. The iPhone Simulator window opens and the main app runs fine there. I've checked that my deployment targets are the same across app and watchkit components (I've tried setting them all to 8.2 and then 8.3 -- the latter doesn't work for reasons others have noted). I've verified that all my bundle ID information is correct and consistent across the app and watchkit components; same for version and build numbers. I've tried using versions 8.2 and 8.3 of the simulator. Nothing works: I can't get the watch window to appear. This began after downloading Xcode v. 6.3.1. Eager for guidance. Thanks in advance to anyone who can help!