Open Radar

 
Reproducible builds:
The bug exists in iOS 14.5+ simulators and devices.

Expected behavior:
I should be able to programmatically control the flow of multiple NavigationLinks destinations (within the same View) using `selection` and `tag`.

Unexpected behavior:
When a third NavigationLink is added to a SwiftUI View, the second NavigationLink will redirect back to the NavigationView root and not to the third NavigationLink destination.

Notes:

I've included a SwiftUI test that should fail (thus reproducing) the bug when running the XCUITest suite in an iOS 14.5 simulator. This XCUITest suite passes when running in an iOS 14.3 simulator.

```swift
import XCTest

class AwesomeAppUITests: XCTestCase {

  func test_whenUserTapsThroughMoreThanTwoScreens_itShouldTakeThemToLastScreen() {
    let app = XCUIApplication()
    app.launch()

    XCTAssertTrue(app.staticTexts["First screen"].exists)
    app.buttons["Tap me!"].tap()

    XCTAssertTrue(app.staticTexts["Second screen"].exists)
    app.buttons["Tap me, again!"].tap()

    XCTAssertTrue(app.staticTexts["Third screen"].exists)
    app.buttons["One more time..."].tap()

    XCTAssertTrue(app.staticTexts["Final screen"].exists)
  }
}
```

```swift
import SwiftUI

struct ButtonView: View {
  let message: String
  let buttonTitle: String
  let onTap: () -> Void

  var body: some View {
    VStack {
      Text(message).padding()

      Button(action: { onTap() }) {
        Text(buttonTitle)
      }
    }
  }
}

struct ContentView: View {
  @State private var selection: String?

  var body: some View {
    NavigationView {
      VStack {
        ButtonView(
          message: "First screen",
          buttonTitle: "Tap me!",
          onTap: { self.selection = "view-2" }
        )

        NavigationLink(
          destination: ButtonView(
            message: "Second screen",
            buttonTitle: "Tap me, again!",
            onTap: { self.selection = "view-3" }
          ),
          tag: "view-2",
          selection: self.$selection
        ) { EmptyView() }

        NavigationLink(
          destination: ButtonView(
            message: "Third screen",
            buttonTitle: "One more time...",
            onTap: { self.selection = "view-4" }
          ),
          tag: "view-3",
          selection: self.$selection
        ) { EmptyView() }

        NavigationLink(
          destination: Text("Final screen"),
          tag: "view-4",
          selection: self.$selection
        ) { EmptyView() }
      }
    }
  }
}
```