Keeping Native Advance Ad in ArrayList is not possible? ( Android Admob / JAVA )

Question

I want to integrate the Native Advance Ad into my RecyclerView. My app shows ad in every 6 items when you scroll down the display. To avoid a lot of ad downloading, I tried to load UnifiedNativeAd 5 times when the RecyclerView shows up, and push these ads into an ArrayList.

As the user scrolls down the display, then onBindViewHolder is called, my app gets an ad from the ArrayList and displays 1st ad, 2nd ad..., and after 5th ad, it returns to show the 1st ad.

I already wrote most of the code using RecyclerView.Adapter and it works fine if you don't mind the content of the ad.

The problem is that, when you return to show 1st ad, only the media content of the ad is different from that of displayed before. Other information, like headline, body, advertiser, is correct. I am not sure why this happens. The summary of the situation is as follows;

My expectation:

          MediaContent    Other(HeadLine, etc)  
1st ad      Ad - A          Ad - A  
2nd ad      Ad - B          Ad - B  
3rd ad      Ad - C          Ad - C  
4th ad      Ad - D          Ad - D  
5th ad      Ad - E          Ad - E  
6th ad      Ad - A          Ad - A  
7th ad      Ad - B          Ad - B  
8th ad      Ad - C          Ad - C  
9th ad      Ad - D          Ad - D  
10th ad      Ad - E          Ad - E  

Problem:

1st ad      Ad - A          Ad - A  
2nd ad      Ad - B          Ad - B  
3rd ad      Ad - C          Ad - C  
4th ad      Ad - D          Ad - D  
5th ad      Ad - E          Ad - E  
6th ad      Ad - E          Ad - A←From this row, MediaContent is random  
7th ad      Ad - A          Ad - B  
8th ad      Ad - A          Ad - C  
9th ad      Ad - B          Ad - D  
10th ad     Ad - C          Ad - E  

Do we have a display ad immediately after loading ads? Is it not appropriate to buffer UnifiedNativeAd in ArrayList? Does anyone have a better idea to show UnifiedNativeAd in the RecyclerView with saving CPU resource and network traffic?