I replaced a Set<MyClass> with Array<MyClass> and everything works, otherwise it appears to miscompile and crash.
Xcode is just completely broken now and often reports errors that don't exist or doesn't report any when they do, so I don't know how meaningful this is, but it says Cannot use a value of protocol type in embedded Swift. The compiler doesn't mind though and just quietly compiles my code.
But, I am not doing that, I am actually inserting a class.
Is there a way to implement a custom panic handler function for Swift, otherwise I can't provide any more details about this error, I can't exactly attach a debugger to wasm.