I'm having a similar lock-up using Objective-C++ ; I'm not sure the C++ portion is relevant, but I don't think that Swift is required for the problem. The test I'm seeing hang has been in my codebase since June 2009 with no recent changes. I do link with some Swift code, but it isn't used in these tests. I have a number of tests that run as part of my build process and I've not had problems before 14.3. However, with this version it's about a 50% chance that one of my test binaries will lock up when run from the GUI. Running through fastlane or directly through xcode-build. I do not see these problems on M1 or M2 Macs in our build farm, but I do see it on my x86_64-based MacPro. I've filed Feedback #FB12154691 on this issue.