UnityAds only showing real ads, no test ads

In one app everything works fine (I get test and when needed and real ads in production).
In a second app, I tried many things:
- In Services -> Advertising -> Test Mode check box
- In code, Advertisement.Initialzie(testMode=true)
- My devices are registered as test devices in the Operate portal

Again - in one app (same devices), I see test ads.
But in the new app, I only get real ads.

How come?

 

Init code:

Code (CSharp):

1.    
2.  
3.             Advertisement.AddListener(this);
4.             Advertisement.Initialize(gameId, testMode);
5.             Advertisement.Banner.SetPosition(BannerPosition.BOTTOM_CENTER);
6.  

Advertisement package: 3.4.4
Unity: 2019.3.2f1

Not sure which logs I should look for. In the console there aren't any errors or warnings. Everything works just fine, except that I'm getting real ads instead of test ads, even when testMode is true, even when Services Test Mode is true, and even though my devices are setup as test devices in the web portal (and properly show test ads in another app).

 

Getting the same issue yet again in another app - no test ads, only real ones. Despite the device being registered as a test device.