Admob banner not showing after the first time it's loaded

Question

The admob banner loads the first time and is shown , but after I navigate to the other fragment and tap back it doesn't load again. ss

 class MainFragment : Fragment() {
   private lateinit var adView: AdView
    private var initialLayoutComplete = false
    private val adSize: AdSize
        get() {
            val windowMetrics =  WindowMetricsCalculator.getOrCreate().computeCurrentWindowMetrics(requireActivity())
            val bounds = windowMetrics.bounds

            var adWidthPixels = binding.adContainerView.width.toFloat()

            // If the ad hasn't been laid out, default to the full screen width.
            if (adWidthPixels == 0f) {
                adWidthPixels = bounds.width().toFloat()
            }

            val density = resources.displayMetrics.density
            val adWidth = (adWidthPixels / density).toInt()
            return AdSize.getCurrentOrientationAnchoredAdaptiveBannerAdSize(requireContext(), adWidth)
        }
  override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        _binding = FragmentMainBinding.inflate(inflater, container, false)
        val view = binding.root
        Log.d("lifecycleMain","onCreateView main fragment")

        recyclerView = binding.recyclerView
        recyclerAdapter = RingtonesAdapter(viewModel.ringtoneList, requireContext()) { ringtone ->
       val action = MainFragmentDirections.actionMainFragmentToCustomizeFragment(ringtone)
            findNavController().navigate(action)
        }
        recyclerView.adapter = recyclerAdapter
        recyclerView.layoutManager =
            LinearLayoutManager(requireContext(), LinearLayoutManager.VERTICAL, false)

        loadAdaptiveBanner()
        return view
    }

 private fun loadAdaptiveBanner(){

        adView = AdView(requireContext())
        binding.adContainerView
            .addView(adView)
        binding.adContainerView
            .viewTreeObserver.addOnGlobalLayoutListener {
                if (!initialLayoutComplete) {
                    initialLayoutComplete = true
                    loadBanner()
                }
            }
    }
    private fun loadBanner() {
        adView.adUnitId = getString(R.string.banner_id)
        adView.setAdSize(adSize)
        val adRequest = AdRequest
            .Builder()
            .build()

        adView.loadAd(adRequest)
    }

I'm using the navigation component and each time it navigates to the another fragment it destroys the main fragment it navigated from , so it might be because of that but didn't find how to stop from doing that.but knowing it's my load function are in the onCreateView() the banner should be loaded again .

this is my nav_graph

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/nav_graph"
    app:startDestination="@id/mainFragment">
    <fragment
        android:id="@+id/mainFragment"
        android:name="com.example.kotlinrings.MainFragment"
        android:label="fragment_main"
        tools:layout="@layout/fragment_main"
        >
        <action
            android:id="@+id/action_mainFragment_to_customizeFragment"
            app:destination="@id/customizeFragment"
            app:enterAnim="@android:anim/fade_in"
            app:exitAnim="@anim/nav_default_exit_anim"
            app:popEnterAnim="@anim/nav_default_enter_anim"
            app:popExitAnim="@anim/nav_default_exit_anim"
            />
    </fragment>
    <fragment
        android:id="@+id/customizeFragment"
        android:name="com.example.kotlinrings.CustomizeFragment"
        android:label="fragment_customize"
        tools:layout="@layout/fragment_customize"
        >
        <argument
            android:name="RINGTONE"
            app:argType="com.example.ring.data.Ringtone" />
    </fragment>
</navigation>