Banners are not working most of the time

I added Unity Monetization SDK 3.3.0 to my project and using interstitials and rewarded videos. But my banners are not working. With the same code I've managed to see the ad 3 or 4 times but other than that banner is not showing eventhough Advertisement.IsReady(placementId) returns true

I have tried:
Changing the testMode for true and false,
Uploaded the app to alpha and test there,
Using Advertisement.Initialize with enablePerPlacementLoad and showing the banners with load callback,(Even it says Load API is in closed beta)
Using Advertisement.Banner.isLoaded to check banner ready status,

None of them fix my problem, like I said I have managed to see the banner for 3-4 times (like once a day or something) but after restarting the app I can not see them anymore. I only call the Show method after Ad is ready and I am really curious if I am doing something wrong.

Documentation was also not really helpful about the banners so I wanted to ask here.

I was suspecting about Unity Ads fillrate for the banners, can anyone help me with this?

(I am using UniRx rather than coroutines)

Code (CSharp):

1. void Start()
2.     {
3.         Advertisement.Initialize(gameId, testModeEnabled);
4.         Advertisement.AddListener(this);
5.         DontDestroyOnLoad(gameObject);
6.     }
7.  
8.     public static void ShowBanner(string placementId, BannerPosition position)
9.     {
10.         bannerDisposable = Observable.Timer(TimeSpan.FromSeconds(0.5f)).Repeat().Subscribe(delegate(long l)
11.         {
12.             Debug.Log("Trying to Load");
13.             if (Advertisement.IsReady(placementId))
14.             {
15.                 Debug.Log($"Banner Loaded : {placementId}");
16.                 Advertisement.Banner.SetPosition(position);
17.                 Advertisement.Banner.Show(placementId);
18.                 bannerDisposable.Dispose();
19.             }
20.         });
21.     }

 

I've found the problem for anyone wondering why their banners are not working.

I logcat the device to check for native logs and saw that there is no fill rate for the banners. What I understand is Unity Ads can not provide enough fill rate and for what it has it is mainly focused on US region.

Hope it will help.