Xcode storyboard: Internal error. Please file a bug

Question

While editing in the storyboard, specifically assigning a view controller to a specific class, I suddenly encountered this error when I wanted to run the project.

Ma

Answer 1

Just ran into this error, and it coincided with non-available iOS versions showing for the wrong Xcode (e.g., iOS 11.2 showing for Xcode 8.2.1, which is not possible for iOS Simulators).

Solution was to delete /Library/Developer/CoreSimulator, e.g.,

rm -rf /Library/Developer/CoreSimulator

In theory you should be able to run xcrun simctl delete unavailable but that didn't work in this case.

Note Found this issue on Xcode 8.2.1, but 9.2 was also installed.