Well.. I did an NVRAM restart (cmd+opt+P+R) - and it solved the issue! as well as re-setting the SMC on my 2015 MacBook Air.. Wow.. that fixed it all.. My MacBook Air has also been getting very very hot since updating to Big Sur.. will see if the above re-sets fixed that as well. Hope this helps all.

I have a 2016 MacBook air 16gig Ram, plenty of room on the SSD, and yet after the update yesterday 15th Dec, Xcode is running terrible. It has never been a rocket on my simple Macbook Air, but it's been very useable. However it is extremely slow now, to a point where it's very frustrating and dissapointing.

Hi,I am getting same similar error.. as below.. Hey hfgjd above, not sure how to find "Module" and to click "Current Product Module"..Cant find that area and selection.Hope you can help or send me a screen shot... please !Thanks !2020-05-02 09:27:50.813395+1000 Ham Log It[1148:40369] [error] warning: Multiple NSEntityDescriptions claim the NSManagedObject subclass 'Things' so +entity is unable to disambiguate.CoreData: warning: Multiple NSEntityDescriptions claim the NSManagedObject subclass 'Things' so +entity is unable to disambiguate.2020-05-02 09:27:50.813787+1000 Ham Log It[1148:40369] [error] warning: 'Things' (0x600001b88160) from NSManagedObjectModel (0x600000f9f7f0) claims 'Things'.CoreData: warning: 'Things' (0x600001b88160) from NSManagedObjectModel (0x600000f9f7f0) claims 'Things'.2020-05-02 09:27:50.814055+1000 Ham Log It[1148:40369] [error] warning: 'Things' (0x600001b816b0) from NSManagedObjectModel (0x600000fa4f00) claims 'Things'.CoreData: warning: 'Things' (0x600001b816b0) from NSManagedObjectModel (0x600000fa4f00) claims 'Things'.2020-05-02 09:27:50.814425+1000 Ham Log It[1148:40369] [error] error: +[Things entity] Failed to find a unique match for an NSEntityDescription to a managed object subclassCoreData: error: +[Things entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass