diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java b/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java
index b4acd60461829..ffc56b6f6106d 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java
@@ -727,10 +727,6 @@ public final class SplitLayout implements DisplayInsetsController.OnInsetsChange
         getRefBounds2(mTempRect);
         t.setPosition(leash2, mTempRect.left, mTempRect.top)
                 .setWindowCrop(leash2, mTempRect.width(), mTempRect.height());
-        // Make right or bottom side surface always higher than left or top side to avoid weird
-        // animation when dismiss split. e.g. App surface fling above on decor surface.
-        t.setLayer(leash1, 1);
-        t.setLayer(leash2, 2);
 
         if (mImePositionProcessor.adjustSurfaceLayoutForIme(
                 t, dividerLeash, leash1, leash2, dimLayer1, dimLayer2)) {
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java b/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java
index 77939c7c69645..b77c9b5840c89 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java
@@ -468,26 +468,10 @@ public class StageCoordinator implements SplitLayout.SplitLayoutHandler,
                     RemoteAnimationTarget[] wallpapers,
                     RemoteAnimationTarget[] nonApps,
                     final IRemoteAnimationFinishedCallback finishedCallback) {
-                boolean openingToSide = false;
-                if (apps != null) {
-                    for (int i = 0; i < apps.length; ++i) {
-                        if (apps[i].mode == MODE_OPENING
-                                && mSideStage.containsTask(apps[i].taskId)) {
-                            openingToSide = true;
-                            break;
-                        }
-                    }
-                } else if (mSideStage.getChildCount() != 0) {
-                    // There are chances the entering app transition got canceled by performing
-                    // rotation transition. Checks if there is any child task existed in split
-                    // screen before fallback to cancel entering flow.
-                    openingToSide = true;
-                }
-
-                if (isEnteringSplit && !openingToSide) {
+                if (isEnteringSplit && mSideStage.getChildCount() == 0) {
                     mMainExecutor.execute(() -> exitSplitScreen(
-                            mSideStage.getChildCount() == 0 ? mMainStage : mSideStage,
-                            EXIT_REASON_UNKNOWN));
+                            null /* childrenToTop */, EXIT_REASON_UNKNOWN));
+                    mSplitUnsupportedToast.show();
                 }
 
                 if (finishedCallback != null) {
@@ -572,26 +556,10 @@ public class StageCoordinator implements SplitLayout.SplitLayoutHandler,
                     RemoteAnimationTarget[] wallpapers, RemoteAnimationTarget[] nonApps,
                     IRemoteAnimationFinishedCallback finishedCallback,
                     SurfaceControl.Transaction t) {
-                boolean openingToSide = false;
-                if (apps != null) {
-                    for (int i = 0; i < apps.length; ++i) {
-                        if (apps[i].mode == MODE_OPENING
-                                && mSideStage.containsTask(apps[i].taskId)) {
-                            openingToSide = true;
-                            break;
-                        }
-                    }
-                } else if (mSideStage.getChildCount() != 0) {
-                    // There are chances the entering app transition got canceled by performing
-                    // rotation transition. Checks if there is any child task existed in split
-                    // screen before fallback to cancel entering flow.
-                    openingToSide = true;
-                }
-
-                if (isEnteringSplit && !openingToSide && apps != null) {
+                if (isEnteringSplit && mSideStage.getChildCount() == 0) {
                     mMainExecutor.execute(() -> exitSplitScreen(
-                            mSideStage.getChildCount() == 0 ? mMainStage : mSideStage,
-                            EXIT_REASON_UNKNOWN));
+                            null /* childrenToTop */, EXIT_REASON_UNKNOWN));
+                    mSplitUnsupportedToast.show();
                 }
 
                 if (apps != null) {
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java b/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java
index ead0bcd15c73b..a841b7f96d3c5 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java
@@ -220,20 +220,12 @@ class StageTaskListener implements ShellTaskOrganizer.TaskListener {
                 mCallbacks.onNoLongerSupportMultiWindow();
                 return;
             }
-            if (taskInfo.topActivity == null && mChildrenTaskInfo.contains(taskInfo.taskId)
-                    && mChildrenTaskInfo.get(taskInfo.taskId).topActivity != null) {
-                // If top activity become null, it means the task is about to vanish, we use this
-                // signal to remove it from children list earlier for smooth dismiss transition.
-                mChildrenTaskInfo.remove(taskInfo.taskId);
-                mChildrenLeashes.remove(taskInfo.taskId);
-            } else {
-                mChildrenTaskInfo.put(taskInfo.taskId, taskInfo);
-            }
+            mChildrenTaskInfo.put(taskInfo.taskId, taskInfo);
             mCallbacks.onChildTaskStatusChanged(taskInfo.taskId, true /* present */,
                     taskInfo.isVisible);
-            if (!ENABLE_SHELL_TRANSITIONS && mChildrenLeashes.contains(taskInfo.taskId)) {
-                updateChildTaskSurface(taskInfo, mChildrenLeashes.get(taskInfo.taskId),
-                        false /* firstAppeared */);
+            if (!ENABLE_SHELL_TRANSITIONS) {
+                updateChildTaskSurface(
+                        taskInfo, mChildrenLeashes.get(taskInfo.taskId), false /* firstAppeared */);
             }
         } else {
             throw new IllegalArgumentException(this + "\n Unknown task: " + taskInfo
@@ -267,6 +259,9 @@ class StageTaskListener implements ShellTaskOrganizer.TaskListener {
                 return;
             }
             sendStatusChanged();
+        } else {
+            throw new IllegalArgumentException(this + "\n Unknown task: " + taskInfo
+                    + "\n mRootTaskInfo: " + mRootTaskInfo);
         }
     }
 
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageTaskListenerTests.java b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageTaskListenerTests.java
index b31e20fcc4389..5ee8bf3006a30 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageTaskListenerTests.java
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/splitscreen/StageTaskListenerTests.java
@@ -126,6 +126,12 @@ public final class StageTaskListenerTests extends ShellTestCase {
         verify(mCallbacks).onStatusChanged(eq(mRootTask.isVisible), eq(true));
     }
 
+    @Test(expected = IllegalArgumentException.class)
+    public void testUnknownTaskVanished() {
+        final ActivityManager.RunningTaskInfo task = new TestRunningTaskInfoBuilder().build();
+        mStageTaskListener.onTaskVanished(task);
+    }
+
     @Test
     public void testTaskVanished() {
         // With shell transitions, the transition manages status changes, so skip this test.