Unity ads banner ad works in testing, but disappears on release

I've recently released my first game, called Dreamline to the Google Play store. This game contains a banner ad. In development, the ad showed up as the simple banner saying "This is where your ad will be". All good.

Next, I released the game to the Google Play store. The banner ad was there, but it was always the default "Unity ads" ad. In order to fix this, I went into the Unity dashboard and set the ad test mode to forced false. The dashbord now states "using production ads for all devices" The dashboard says I got 39 impressions, but there are way more requests. (90). Also, when I boot up the game, no ads show up ever, even though I'm connected to the internet.

This is the code I'm using to serve my banner ad:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.Advertisements;
 using UnityEngine.SceneManagement;
 
 public class AdManager : MonoBehaviour
 {
     public string gameId = "3647601";
     public bool testMode = false;
     public string placementID = "bannerAd";
     public Scene activeScene;
     public bool isShowing = false;
 
     private static AdManager instance = null;
     public static AdManager Instance
     {
         get { return instance; }
     }
     // Start is called before the first frame update
 
     private void Awake()
     {
         
         if (instance != null && instance != this)
         {
             Destroy(this.gameObject);
             return;
         }
         else
         {
             instance = this;
         }
         if(activeScene.name == "TestStuff")
         {
             DontDestroyOnLoad(this.gameObject);
         }
     }
 
     void Start()
     {
         Advertisement.Initialize(gameId, testMode);
         StartCoroutine(ShowBannerWhenReady());
     }
 
     IEnumerator ShowBannerWhenReady()
     {
         while (!Advertisement.IsReady(placementID))
         {
             yield return new WaitForSeconds(0.5f);
         }
         Advertisement.Banner.SetPosition(BannerPosition.BOTTOM_CENTER);
         Advertisement.Banner.Show(placementID);
     }
 }

I'm using a dontdestroyonload because every time the player dies, the scene gets reloaded. The dontdestroyonload prevents the ad from reloading as well, which should keep the impression right.

So the question that this all brings me to is: What do I do in order to make my unity ads banner ad show up properly and consistently?