SwiftUI AttributeGraph cycle in playground only

CountingEditorApp.swift

// Put this into an Xcode 12.0 multiplatform app

import SwiftUI

struct ContentView: View {
    @State var text = "Hello!"

    var body: some View {
        VStack {
            TextEditor(text: $text)
            HStack {
                Spacer()
                Text("\(text.count) characters")
            }
        }
    }
}

@main
struct CountingEditorAppApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

CountingEditorPlayground.swift

// Put this into an Xcode 12.0 iOS playground

import SwiftUI
import PlaygroundSupport

struct ContentView: View {
    @State var text = "Hello!"

    var body: some View {
        VStack {
            TextEditor(text: $text)
            HStack {
                Spacer()
                Text("\(text.count) characters")
            }
        }
    }
}

import PlaygroundSupport
PlaygroundPage.current.setLiveView(ContentView())

The first version (in a standalone app) works just fine. The second version in an iOS playground leads to warnings of the form === AttributeGraph: cycle detected through attribute 5336 === in the Xcode debug area and, at the same time, the view is not very responsive and sometimes skips updates.

What is the problem here? This behaviour makes it quite awkward to test (and experiment) with some SwiftUI views in Xcode playgrounds.

@mchakravarty experiencing the same in Xcode 12.4, did you ever find out what was the issue?