Pop enter animation not working with the Jetpack Navigation Component

Question

I have been using the Jetpack Navigation component (2.3.5, although I have tested older versions too) and trying to add transitions between two simple destinations. However, the transition specified with the popEnterAnim attribute doesn't run at all. Instead the re-entering fragment just immediately appears.

I have managed to recreate it with a really simple example. The fragment layouts are just a single TextView.

Main activity

<androidx.fragment.app.FragmentContainerView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/nav_host_fragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:defaultNavHost="true"
    app:navGraph="@navigation/nav_graph" />

class ActivityMain : AppCompatActivity(R.layout.main)

Fragment 1

class Fragment1 : Fragment(R.layout.fragment_1) {

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {

        view.setOnClickListener {

            findNavController().navigate(R.id.action_fragment1_to_fragment2)
        }
    }
}

Fragment 2

class Fragment2: Fragment(R.layout.fragment_2)

Navigation graph

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" android:id="@+id/nav_graph.xml"
    app:startDestination="@id/fragment1">

    <fragment
        android:id="@+id/fragment1"
        android:name="uk.henrytwist.projectsource.Fragment1"
        android:label="MainFragment" >
        <action
            android:id="@+id/action_fragment1_to_fragment2"
            app:destination="@id/fragment2"
            app:enterAnim="@anim/transition_rise_up_enter"
            app:exitAnim="@anim/transition_fade_exit"
            app:popEnterAnim="@anim/transition_fade_pop_enter"
            app:popExitAnim="@anim/transition_rise_up_pop_exit" />
    </fragment>
    <fragment
        android:id="@+id/fragment2"
        android:name="uk.henrytwist.projectsource.Fragment2"
        android:label="Fragment2" />
</navigation>

Answer 1

It turns out that this was actually due to a bug in the AndroidX fragment library (androidx.fragment:fragment:1.3.2) which has now been rectified in version 1.3.3. The changelog confirms the fix:

Fixed a regression introduced in Fragment 1.3.2 which would cause popEnter animations to not run when popping a FragmentTransaction that included a setPrimaryNavFragment operation, such as those used by NavHostFragment. (I38c87, b/183877426)