iOS 8.0.2 Library Not Loaded libswiftCore.dylib

Simply do the following two steps:

1) Delete the App from the device (or simulator)

2) Clean your workspace (CMD+SHIFT+K or via menu Product->Clean)

3) Build and run your app again.

Magically helps every time with all that startup / deploy stuff...

I also often get something like "application not found on device" or signing problems etc. Minutes before everything worked well.

This appears to possibly be a code signing issue on Apple's part, and the issue seems affect apps with embedded frameworks (including non-Swift apps). There are multiple accounts of developers being affected (myself included) who had only submitted an update, without changing any build settings. Some high profile apps appear to have been affected and tickets have been filed with Apple, but there has been no official response from them at this time.

EDIT: This has been confirmed.

Edit:

The app was rejected, after making this change, for the same reason, however, I am confident that the problem has to do with a missing architecture version in the libswiftCore.

I am going to post this as the provisional answer. Xcode 6 Standard architectures exclude armv7s

Notice how the error says: Did find: /path/to/my/app/Frameworks/libswiftCore.dylib

So it did find the lib but it also says: Reason: no suitable image found.

After running lipo against the archived build it didn't contain armv7s in the swift library, or in the app binary. I manually added it per the link above and the binary now contains support for armv7s though the swift library still did not. My app is in expedited review so I should get feedback farily quick. I will follow up when that does happen.