Multiple Tab fragments inside bottom navigation fragment

Actually, it is a common mistake - you're using FragmentManager of your Activity inside the fragment, but since this fragment contains another child fragments you have to use FragmentManager of the fragment itself. So the fix is simple - you just have to change getActivity().getSupportFragmentManager() to getChildFragmentManager() inside your fragments, so the code will be:

private void setupViewPager(ViewPager viewPager) {
    TabViewPagerAdapter adapter = new TabViewPagerAdapter(getChildFragmentManager());
    ...
    ...
    viewPager.setAdapter(adapter);
}

And this should work as expected.