You might get this error after you add a new variable to your C++ code that you want to be accessible in an Unreal Engine Blueprint. This can be done by using the UPROPERTY(EditAnywhere, BlueprintReadWrite) macro. After rebuilding your solution, you probably expect the variable to be available to the Blueprint right away (and it may very well be), but you might be surprised that sometimes you get runtime errors like this not only for the variables that were already Blueprint-accessible and working properly but also the new one(s). Searching the Internet for a solution didn’t offer much help. So, what’s the solution? Although you might expect that building the C++ solution also compiles the Blueprints, this is not always the case. Although Blueprints are turned into C++ classes through a process called Blueprint Nativization, the Blueprints are not always recompiled when you compile the C++ solution. And it seems this is a long-standing problem (or bug). After adding the new Blueprint-accessible variable to your C++ class and compiling it, make sure you recompile the Blueprint itself from the Blueprint Editor. The variable should then be available to the Blueprint.
If you downloaded the Xcode xip file instead of getting the app through the macOS App Store, you also had to decompress the more the 10 GB file in order to get the .app file. You might also have tried to decompress the file using the default app called “Archive Utility”. Not only does this app take a substantial amount of time (hours) to decompress the .xip file, but to your surprise the decompressed Xcode app shows you the error message “Required content for iOS Simulator is missing” or “Required content for tvOS Simulator is missing” once you try to open it. The error is actually due to the way that the xip file has been decompressed. So what’s the solution? Instead of using the “Archive Utility”, simply put the xip file into the Applications folder and use the command line xip utility instead:
# cd /Applications
#xip –expand Xcode_X.X.X.xip
xip: signing certificate was “Software Update” (validation not attempted)
xip: expanded items from “/Applications/ Xcode_X.X.X.xip”
The xip command line utility not only takes much less time than the Archive Utility to decompress the files, but the error message no longer shows up once you run the Xcode app.