[AppBarLayout] Elevation disappears when AppBarLayout is half visible

Description: When AppBarLayout has app:liftOnScroll="true" and its sibling has app:layout_scrollFlags="scroll|enterAlways|snap", the elevation disappears if you stop scrolling when the AppBarLayout is half-visible.

The issue is easy to see if after scrolling up and hiding the AppBarLayout you start scrolling down very slowly.

Expected behavior: Elevation should remain visible even if you stop scrolling when AppBarLayout is half-visible.

Source code:

<com.google.android.material.appbar.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:liftOnScroll="true"
    >
    <com.google.android.material.appbar.MaterialToolbar
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        app:layout_scrollFlags="scroll|enterAlways|snap"
        />
</com.google.android.material.appbar.AppBarLayout>

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    >
</FrameLayout>

Android API version: The problem is reproducible in APIs 16 through 30.

Material Library version: 1.3.0

Device: Android emulators (APIs 16 through 30) and Pixel 2 (API 30).

Inizia riproducendo il problema con l’AppBarLayout, il MaterialToolbar, gli scrolling flags e la configurazione di appbar_scrolling_view_behavior forniti su un emulatore Android. Verifica la elevation fermandoti con l’AppBarLayout parzialmente visibile e considera il problema risolto quando la elevation rimane visibile in quello stato nelle versioni API segnalate.