FullScreenIntent Notification not consistently dismissing keyguard

I'm building a VoIP calling app on Android using the Self Managed Telecom Framework, but I've hit a wall with the incoming call notification when the device is locked/sleeping/whatever it is.

This is my onCreate method in my Activity that gets displayed on an incoming call:

class IncomingCallFullScreenActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Log.d(TAG, "onCreate")

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O_MR1) {
            // For newer than Android Oreo: call setShowWhenLocked, setTurnScreenOn
            setShowWhenLocked(true)
            setTurnScreenOn(true)
            Log.d(TAG, "onCreate(): O_MR1 logic applied")
        } else {
            // For older versions, do it as you did before.
            window.addFlags(
                WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON
                        or WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
                        or WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
                        or WindowManager.LayoutParams.FLAG_ALLOW_LOCK_WHILE_SCREEN_ON
            )

            Log.d(TAG, "onCreate(): PRE O_MR1 logic applied")
        }

        with(getSystemService(Context.KEYGUARD_SERVICE) as KeyguardManager) {
            Log.d(TAG, "onCreate(): Requesting keyguard dismissal")
            requestDismissKeyguard(this@IncomingCallFullScreenActivity, object : KeyguardManager.KeyguardDismissCallback() {
                override fun onDismissError() {
                    Log.d(TAG, "onCreate(): onDismissError")
                }

                override fun onDismissSucceeded() {
                    Log.d(TAG, "onCreate(): onDismissSucceeded")
                }

                override fun onDismissCancelled() {
                    Log.d(TAG, "onCreate(): onDismissCancelled")
                }
            })
        }

        setContentView(R.layout.incoming_call_ringer_screen)
        hideSystemUI()
    }

    private fun hideSystemUI() {
        // Enables sticky immersive mode.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
            window.setDecorFitsSystemWindows(false)
            window.insetsController?.let {
                it.hide(WindowInsets.Type.statusBars() or WindowInsets.Type.navigationBars())
                it.systemBarsBehavior = WindowInsetsController.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE
            }
        } else {
            @Suppress("DEPRECATION")
            window.decorView.systemUiVisibility = (View.SYSTEM_UI_FLAG_FULLSCREEN
                    or View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                    or View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
                    or View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                    or View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                    or View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION)
        }
    }
}

And this works, but in I'd say 20% of cases, the keyguard doesn't dismiss properly. Instead of just showing my incoming call intention, it'll show the keyguard on top of it. If I press "return to call" on it, it'll work fine - if it dismiss it it works fine. But in those about 20% of cases, it doesn't dismiss properly as expected.

I've done my majority of testing on an Android X device, but I've seen it happen on Android 11 as well.

I've tried calling the requestDismissKeyguard function a few different places, such as onStart, onAttachedToWindow - but all with the same results.

I've got a feeling it's because this method needs to be called at some other point in the life cycle, but really I'm at a loss for what to try at this point.

This never happens in the emulator. Only on physical devices (I've tested on a Samsung Galaxy S9 and S21 Ultra).

The Android docs states that if the activity is in a trusted state, the keyguard will dismiss immediately. I can only assume that this means that some times this activity isn't in a trusted state.

This seems to be more prone to happen if the device has been locked / screen turned off for a little while.

In 80% of cases, the incoming call notification displays a-ok!

But some times the keyguard doesn't fully dismiss!