I'm also having the same issue on the latest iOS 14.2 beta.

xcodebuild has a new option -enablePerformanceTestsDiagnostics YES that collects diagnostics for Performance XCTests. The option collects a ktrace file for non-XCTMemoryMetrics, and a series of memory graphs for XCTMemoryMetrics. xcodebuild attaches diagnostics to the generated xcresult bundle. Note that memory graph collection isn’t available in simulated devices. (64495534) xcode-13-release-notes