Stuck with updating adapter

I've stucked with pretty simple thing - adapter updating.

I have Fragment with Adapter1 inside which creating N items (vertical RecyclerView). Every item is Adapter2 which has NN items (horizontal RecyclerView). When scrolling Adapter2, I'm loading more items for Adapter2 in Fragment's method.

Let's say this is code in Adapter2:

// loading more items for Adapter2
if(position == getItemCount() - 1){
    mFragment.loadMore(arg1, arg2, arg3);
}

And this is code from Fragment:

public void loadMoreModule(args){
    ExecutorService executor = Executors.newSingleThreadExecutor();
    Handler handler = new Handler(Looper.getMainLooper());
    executor.execute(() -> {
        // background work here
        downloadData(arg1, arg2, arg3);

        handler.post(() -> {
            // UI Thread work here
            Adapter1.notifyDataSetChanged();
            Adapter1.RecyclerViewForAdapter2Item.scrollTo(position);
        });
    });
}

scrollTo() like I understood executing before notifyDataSetChanged() or notifyItemRangeChanged(start, size) is done so when new data loaded I getting a problem - by default RecyclerViewForAdapter2Item scrolled to the first item.

Adapter1 sample code:

    Adapter1 {
        private Adapter2 adapter2;

        onBindViewHolder(){
            adapter2 = new Adapter2(args);
        }
   }

loaded data and position for scrollTo() have right values.
Due to some issues when working with backend API I must update the whole Adapter1 and try to scroll. I can't update Adapter2 item only.
Should be redone work with API so I could update Adapter2 or I can update it somehow now?

First of all, Is there any way around instead updated the wholde Adapter? NotifyDataSetChanged is not a correct way to update your adapter, you can find the differences between your currently loaded data and the new loaded data and then you can update only the items who change, this way you won't have to scroll the list by yourself, the scroll position will be maintained.

Currently when you updated the whole adapter calling notifyDataSetChanged the adapter is recreating all the items inside, (also your nested RecyclerView). So basicly if the items inside are being recrated, the scroll position will be lost.