I also tried on iPadOS 26.5.2 with Xcode 26.6 and hit the same issue (SwiftUI instrument causes all instruments to report nothing on stop). On-device logs show swiftuitraced never launches (launchd reports com.apple.swiftuitracingsupport.xpc doesn't exist), and DTServiceHub crashes in SwiftUITracingSupport at recording stop while draining the session, which is why other instruments' lanes come up empty too. Filed as FB23807146 with traces, crash reports, and a sysdiagnose; see also thread 812557. (That feedback is from a different account; sorry, didn't realize I was logged in on a separate Apple ID.)

I'm having the same issue. Running on my iPhone 17 (iOS 27.0 public beta).