Transition Manager - Sliding a view out is not working as wanted

I'm trying to slide this view in and out using Transition + Transition manager, however when hitting the hide button to make the view GONE it doesn't have the sliding animation. However, the show button does have the sliding in animation to make the view VISIBLE again.

    @OnClick(R.id.testBtn)
        public void onTestBtnClick(){
            //hide
            Transition transition = new Slide(Gravity.START);
            transition.setDuration(600);

            TransitionManager.beginDelayedTransition(mParentLayout, transition);
            mLayout.setVisibility(View.GONE);
        }

        @OnClick(R.id.testBtn2)
        public void onTestBtn2Click(){
            //show
            Transition transition = new Slide(Gravity.START);
            transition.setDuration(600);

            TransitionManager.beginDelayedTransition(mParentLayout, transition);
            mLayout.setVisibility(View.VISIBLE);
        }

I've tried changing the gravity of testBtn2 to Gravity.END, but that causes it to slide all the way starting from the right side of the screen.

Here's the layout:

<androidx.constraintlayout.widget.ConstraintLayout
    android:id="@+id/main_activity_root_view"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/testBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        android:text="Hide"
        app:layout_constraintStart_toStartOf="parent"/>

    <Button
        android:id="@+id/testBtn2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toEndOf="@id/testBtn"
        android:text="show"
        />

    <LinearLayout
        android:id="@+id/layout"
        android:orientation="vertical"
        android:layout_width="100dp"
        android:layout_height="250dp"
        android:background="@drawable/background_side_bar_corners"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>

Not sure whats wrong with your code. i have created a sample, just try the code below it working fine. make sure to add android:visibility="gone" for panel view in layout so that its hidden at first launch.

public class MainActivity extends AppCompatActivity {
boolean isShowing = false;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_damm_activty);
    findViewById(R.id.testBtn).setOnClickListener(v -> {
        showSlidingPanel(!isShowing);
    });
}

private void showSlidingPanel(boolean show) {
    ViewGroup parent = findViewById(R.id.main_activity_root_view);
    View layout = findViewById(R.id.layout);
    Transition transition = new Slide(Gravity.START);
    transition.setDuration(450);
    transition.addTarget(R.id.layout);
    transition.setInterpolator(new AccelerateDecelerateInterpolator());
    TransitionManager.beginDelayedTransition(parent, transition);
    layout.setVisibility(show ? View.VISIBLE : View.GONE);
    isShowing = show;
}
}