Call adapter.notifyItemChanged(position) but itemView at position+1 dismissed

Question

I had a layout like this:

<recyclerView1>
    <itemView1>
        ...
        <recyclerView2>
            <itemView2/>
            <itemView2/>
            ...
        </>
    </>
    <itemView1 .../>
    <itemView1 .../>
    ...
</>

It's a ReyclerView nested another RecyclerView.

When recyclerView1.itemView(pos) in the screen, and recyclerView1.itemView(pos+1) out of the screen,

I tap recyclerView1.itemView(pos) to call recyclerView1.adapter.notifyItemChanged(pos),

all itemView2 in recyclerView1.itemView(pos+1).recyclerView2 are dismissed.

Step:

1. itemView(pos) and itemView(pos+1)

2. scroll down to make itemView(pos+1) out of screen.

3. tap itemView(pos) to call recyclerView1.adapter.notifyItemChanged(pos).

4. scroll up to show itemView(pos+1).

5. all itemView2 in recyclerView1.itemView(pos+1).recyclerView2 are dismissed.

I don't know why.anyway to keep itemView2 in itemView(pos+1) showing?

hope for suggestion.:)