The 100% worked solution is: Turn you Apple Watch off, and every thing is OK. PS: Sold it on eBay may work fine I guess :)

Today is April 24 2022 and this problem is still existing on the newest Xcode 12.3.1. The "seconds" saved by your complier optimized are all payed back with "minutes". So I guess we iOS developers should NOT purchase any Apple Watch in the future?

Updated to Xcode 12.0.1, problem NOT solved. 😂 One of the most weird bug I'v ever met on Xcode.