MyClass is unavailable: cannot find Swift declaration for this class – Release Build Only

If MyClass is inside a dynamic framework (Cocoa Touch Framework), It is likely that you’re using a build with wrong architecture. To check, browse your MyClass.framework in finder, and check Modules/AirServiceKit.swiftmodule. There should be something like x86_64.swiftmodule or arm64.swiftmodule, if you’re using simulator there should be x86, or arm if you’re building for device.