For some reason Xcode has started showing this message last night. Even loading a new SpriteKit project and running it unmodified gets the error.

The scene loads, but is unresponsive.

I've also tried modifying the program by removing the default scene and creating a new one; new SKS file has the same issue. Existing projects still compile and load properly, however.

Considering the default template isn't working out of the box anymore, is this an Xcode update gone wrong, or is there something that can be done to force it to realize the class does, in fact, exist? Restarting the computer had no effect on the issue.