Custom rotor is always playing end-of-list sound

I have a custom rotor that changes the skim speed of the skim forward/backward feature of my audio player. The rotor works, but it's always playing an end-of-list sound.

Here is the code:

    // Member variables
    private let accessibilitySeekSpeeds: [Double] = [10, 30, 60, 180]  // seconds
    private var accessibilitySeekSpeedIndex: Int = 0

    func seekSpeedRotor() -> UIAccessibilityCustomRotor {
        UIAccessibilityCustomRotor(name: "seek speed") { [weak self] predicate in
            guard let self = self else { return nil }
            
            let speeds = accessibilitySeekSpeeds
            switch predicate.searchDirection {
            case .previous:
                accessibilitySeekSpeedIndex = (accessibilitySeekSpeedIndex - 1 + speeds.count) % speeds.count
            case .next:
                accessibilitySeekSpeedIndex = (accessibilitySeekSpeedIndex + 1) % speeds.count
            @unknown default:
                break
            }
            
            // Return the currently selected speed as an accessibility element
            let accessibilityElement = UIAccessibilityElement(accessibilityContainer: self)
            let currentSpeed = localizedDuration(seconds: speeds[accessibilitySeekSpeedIndex])
            accessibilityElement.accessibilityLabel = currentSpeed + " seek speed"
            UIAccessibility.post(notification: .announcement, argument: currentSpeed + " seek speed")
            return UIAccessibilityCustomRotorItemResult(targetElement: accessibilityElement, targetRange: nil)
        }
    }

The returned accessibility element isn't read out, and instead an end-of-list sound is played. I can announce the change manually using UIAccessibility.post, but it still plays the end-of-list sound.

How can I prevent the rotor from playing the end-of-list sound?