I believe I'm still seeing this in beta 5: this SDK is not supported by the compiler (the SDK is built with 'Apple Swift version 5.5 effective-4.2 (swiftlang-1300.0.31.1 clang-1300.0.29.1)', while this compiler is 'Apple Swift version 5.7 effective-4.2 (swiftlang-5.7.0.123.8 clang-1400.0.29.50)')