I am getting the following error which was NOT present on Xcode 11. I have trouble reproducing the issue since this is a large project and I can't pinpoint the file in which it happens. The error doesn't say which file it is. Apple Swift version 5.3 (swiftlang-1200.0.29.2 clang-1200.0.30.1) While reading from 'Swift' 0 swift          0x0000000107e1c865 llvm::sys::PrintStackTrace(llvm::rawostream&) + 37 1 swift          0x0000000107e1b865 llvm::sys::RunSignalHandlers() + 85 2 swift          0x0000000107e1ce1f SignalHandler(int) + 111 3 libsystemplatform.dylib 0x00007fff73ac35fd sigtramp + 29 4 libsystemplatform.dylib 0x00007ffe00000002 sigtramp + 18446744067473918498 5 swift          0x0000000107df11bc llvm::vfs::VFSFromYamlDirIterImpl::incrementImpl(bool) + 156 6 swift          0x0000000107df10fd llvm::vfs::VFSFromYamlDirIterImpl::VFSFromYamlDirIterImpl(llvm::Twine const&, std::1::wrapiter<std::1::uniqueptr<llvm::vfs::RedirectingFileSystem::Entry, std::1::defaultdelete<llvm::vfs::RedirectingFileSystem::Entry> >>, std::1::wrapiter<std::1::uniqueptr<llvm::vfs::RedirectingFileSystem::Entry, std::1::defaultdelete<llvm::vfs::RedirectingFileSystem::Entry> >>, bool, llvm::vfs::FileSystem&, std::1::errorcode&) + 141 7 swift          0x0000000107dee3d8 llvm::vfs::RedirectingFileSystem::dirbegin(llvm::Twine const&, std::1::errorcode&) + 216 8 swift          0x0000000107a5c628 clang::HeaderSearch::loadSubdirectoryModuleMaps(clang::DirectoryLookup&) + 264 9 swift          0x0000000107a5c264 clang::HeaderSearch::lookupModule(llvm::StringRef, llvm::StringRef, bool) + 916 10 swift          0x0000000107a5be39 clang::HeaderSearch::lookupModule(llvm::StringRef, bool, bool) + 105 11 swift          0x0000000104958b77 swift::ClangImporter::Implementation::loadModuleClang(swift::SourceLoc, llvm::ArrayRef<swift::Located<swift::Identifier> >) + 103 12 swift          0x000000010495969b swift::ClangImporter::loadModule(swift::SourceLoc, llvm::ArrayRef<swift::Located<swift::Identifier> >) + 75 13 swift          0x00000001043fb766 swift::ModuleFile::getModule(llvm::ArrayRef<swift::Identifier>, bool) + 534 14 swift          0x000000010444bdeb swift::ModuleFile::associateWithFileContext(swift::FileUnit*, swift::SourceLoc, bool) + 1787 15 swift          0x00000001044b455d swift::SerializedModuleLoaderBase::loadAST(swift::ModuleDecl&, llvm::Optional<swift::SourceLoc>, llvm::StringRef, std::1::uniqueptr<llvm::MemoryBuffer, std::1::defaultdelete<llvm::MemoryBuffer> >, std::1::uniqueptr<llvm::MemoryBuffer, std::1::defaultdelete<llvm::MemoryBuffer> >, std::1::uniqueptr<llvm::MemoryBuffer, std::1::defaultdelete<llvm::MemoryBuffer> >, bool, bool) + 1037 16 swift          0x00000001044b6a59 swift::SerializedModuleLoaderBase::loadModule(swift::SourceLoc, llvm::ArrayRef<swift::Located<swift::Identifier> >) + 825 17 swift          0x0000000104acb2b6 swift::ASTContext::getStdlibModule(bool) + 406 18 swift          0x0000000103abe869 swift::CompilerInstance::performSemaUpTo(swift::SourceFile::ASTStage_t) + 3497 19 swift          0x000000010398032d swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 6845 20 swift          0x0000000103904c37 main + 1255 21 libdyld.dylib      0x00007fff738cacc9 start + 1 22 libdyld.dylib      0x0000000000000084 start + 18446603338577564604 error: Segmentation fault: 11

When you have an HKWorkoutSession started on watchOS6 and call session.pause() it does not change the state to .paused and it stays at .running and therefore does not call the delegate that the state has changed, because it hasn't, and it breaks the app. This issue does not occur on watchOS5, only on watchOS6.