I got this exception running JankAggregatorActivity on an API 24 emulator:

java.lang.IllegalArgumentException: attempt to remove OnFrameMetricsAvailableListener that was never added
at android.view.View.removeFrameMetricsListener(View.java:5560)
at android.view.Window.removeOnFrameMetricsAvailableListener(Window.java:863)
at androidx.metrics.performance.DelegatingFrameMetricsListener.onFrameMetricsAvailable(JankStatsApi24Impl.kt:226)
at android.view.FrameMetricsObserver.notifyDataAvailable(FrameMetricsObserver.java:72)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:323)
at android.os.Looper.loop(Looper.java:136)
at android.os.HandlerThread.run(HandlerThread.java:61)

To repro, run the app, then tap the home button. This disables jank stats tracking, which ends up removing a delegate listener and then the delegator itself (apparently twice).

It's not 100%, but it's fairly frequent.
Looks like there are two places in JankStatsApi24Impl where we remove the delegator listener from the window, in removeFrameMetricsListenerDelegate() (when we have removed the last delegate) and in OnFrameMetricsAvailable (when we detect a delegates list size of 0)