"Install of Apple Watch Application never finished" Error when deploying watch kit app to device

I keep running into this as well with Xcode 7 beta and iOS 9 / watchOS 2 simulators.

One solution that worked for me was to reset and restart both simulators, but it didn't work reliably. So I tried some other things, and what eventually started to work reliably for me was:

1. Go to the "Apple Watch" companion app on the iOS simulator.
2. Click your app's name.
3. Toggle "Show App on Apple Watch" switch as shown in the screenshot below. (turn it off, and back on again)
4. Run the app again from Xcode.

Well with much testing and fooling around, I was able to fix the problem.

There was a mix of the error above as well as the usual verification error.

I had to double check and triple check that all 3 of the developer provisioning profiles for watch ext, watch app, and the app were up to date with the updated Watch UDID device.

Note: For debugging watch apps, I have found that you seem to have to select to run the app from your watch and then the debugger will trigger

I had this problem with the simulator. I solved it by resetting both simulators (File/"Reset Content and Settings..."). Not sure if I had to be that drastic... deleting the app may have worked also, restarting the simulator didn't.