After investigating this further, I believe the issue to be related to the SquareReaderSDK and a framework called mmMobile. They both have an Event class and Xcode 12 seems to be having some issues with that:
objc: Class Event is implemented in both /Users/user/Library/Developer/CoreSimulator/Devices/B4816790-617D-4DBB-A2EB-9650A6CE43D9/data/Containers/Bundle/Application/8B62D497-C39B-43A4-BEA4-6E4B2F16D61E/APP.app/Frameworks/mmMobileSDK.framework/mmMobileSDK (0x112ab4168) and /Users/user/Library/Developer/CoreSimulator/Devices/B4816790-617D-4DBB-A2EB-9650A6CE43D9/data/Containers/Bundle/Application/8B62D497-C39B-43A4-BEA4-6E4B2F16D61E/APP.app/Frameworks/SquareReaderSDK.framework/SquareReaderSDK (0x10c947c70). One of the two will be used. Which one is undefined.
And this is the error:
Thread 1: "+[Event loadCustomEntityAdditionsInManagedObjectModel:]: unrecognized selector sent to class 0x115c82488"
This seems to indicate that the compiler is using the mmMobileSDK’s Event class instead of the SquareReaderSDK’s and it results in an unrecognized selector error.
Is there any way around this?