Horizontal Scroll Recyclerview in Vertical Recyclerview with CollapsingToolbarLayout

Question

I am building an application that uses a ViewPager2 to scroll horizontally across pages that each have a vertically scrolling content RecyclerView where the first position of each list has a row with a Horizontally scrolling widget such as another RecyclerView or ViewPager2 attached to a Pager Indicator type widget as seen from the below image.

The parent ViewPager2 is a child of a CoordinatorLayout that handles collapsing the top content when the RecyclerView is scrolled Vertically. This ViewPager2 then inflates fragments that are horizontally scrolling. So we have for the parent layout:

-- CoordinatorLayout 
   -- FrameLayout - has appbar scrolling behavior 
      -- ViewPager2
   -- AppBarLayout
      -- CollapsingToolbarLayout
         -- ImageView - background
         -- Toolbar
         -- ConstraintLayout - Holds title and date

The parent ViewPager2 child fragments' layout:

-- FrameLayout
   -- RecyclerView
   -- Pager Indicator 

The first row of the content RecyclerView has the same layout:

-- FrameLayout
   -- RecyclerView
   -- Pager Indicator 

You can see from the above screenshot that on first load the RecyclerView is overlapping the AppBarLayout which is the correct behavior. I added negative marginTop to RecyclerView's parent layout to achieve this effect. I am tracking the AppBarLayout offset changes with a AppBarLayout.OnOffsetChangedListener and as the user scrolls up I am reducing or increasing this negative margin to have the list animate under the AppBarLayout.

The problem I am facing is if I start a vertical scroll from the first item in the list then the AppBarLayout is not getting triggered to start collapsing its content so the content ends up prematurely under the AppBarLayout. See the following screenshot:

I want the AppBarLayout content to start scrolling up as soon as I start the content RecyclerView scroll even if it is initiated from the first position. It seems that the first item's RecyclerView is not alerting the AppBarLayout to start collapsing. If I start the scroll from other items in the RecyclerView the correct behavior is observed. If I drag up and hold from the first row then the bug is also observed.

A good example of the behavior I am trying to achieve is the Google News App where there is a tab of news sections. The following is what I am expecting:

Answer 1

The solution turned out to be simple. If you have a nested RecyclerView or similar container then you have to use:

RecyclerView.setNestedScrollingEnabled(false)