FindViewById is null after device rotation inside FragmentPagerAdapter

Question

I am trying to modify UI elements that are inside a FragmentPagerAdapter on a ViewPager. Everything goes well until I rotate the device. Then, FindViewById returns null and I can't modify the element.

When I rotate the device do I have to keep in mind some operation? FragmentPagerAdapter manages the Fragments when the activity re-creates? runOnUIThread has any implication on this? I am using something wrong?

MainActivity.java

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        ...

        //detect if it was recreating by rotation device
        if(savedInstanceState != null) {
            rotateEvent = savedInstanceState.getBoolean("rotateEvent");
        }


        // Set up the ViewPager with the sections adapter.
        mViewPager = findViewById(R.id.pager);
        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        mViewPager.setAdapter(mSectionsPagerAdapter);
        mViewPager.setOffscreenPageLimit(5);


        tabLayout = findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(mViewPager);

        ...
   }

   /**
     * On Received Status update on UI state
     * @param messageReceived: string received
     */
    public void updateReceivedStatus(final String messageReceived) {

        runOnUiThread(new Runnable() {
            @Override
            public void run() {

                    int idElementToUpdate = getResources().getIdentifier(messageReceived, "id", getPackageName());

                    View element = findViewById(idElementToUpdate); // element is null after rotation

                    //Switch type send different message
                    if (element instanceof RadioGroup) {
                        //obtain id string of radiobutton
                        String radioButtonId = message.replace(":", "_");

                   ...
            }
        }
   }

Thanks in advance.