IAP does not work anymore - onInitialized is not being called after first launch of app

I have moved my project to 2019.1 from 2018.2.20 where everything worked.
For 2019 I also updated IAP to 1.22.
I’m basically using a modified version of IAPDemo.cs…
The first time the app is launched after installation OnInitialized is called which I can see in the log:
“OnInitialized: PASS”
Then all the products show up as intented.
From the 2nd app launch on neighter the OnInitialized nor the OnInitializeFailed callbacks are called.

  • no exception just silence!
    Also, it does not help to delete files from the android/data folder.

I have seen, that the new IAPdemo.cs is different a lot. But shouldn´t it be backwards compatible? It works on iOS without any problems.
So is there anything that has to be changed?

purchaser.cs can be found here: https://forum.unity.com/threads/oninitialized-is-not-called-on-android-when-app-is-launched-again-after-installation.672187/#post-4503562

I found the bug: when using Application.Quit(), which I did, the UnityIAP System does not shut down cleanly and therefore does not initialize on next start. When the app is “swiped” away however, everything is fine on next start.