Bump. Same problem in a Task wrapping URLSession.shared.data(from:). I tried giving it .background priority as the doc for Task.result hinted. Task.checkCancelled() at various points, no effect. Using URLRequest, no effect. PlaygroundPage.current.needsIndefiniteExecution = true, no effect. Importing Foundation, UIKit, or AppKit made no difference, which is kind of crazy, a UIKit playground ought to say it can't find AppKit. The Playground console says: error: execution stopped with unexpected state. error: Execution was interrupted, reason: shared-library-event. Not informative so far in my searches.