State loss on Marshmallow (Android 6) device

I set up this [simplified sample project](https://github.com/johnjohndoe/PhotoViewTest) which configures the _PhotoView_ library in a `Fragment` which is hosted in an `Activity`. I am using [version 1.3.1](https://github.com/chrisbanes/PhotoView/releases/tag/1.3.1) here because I cannot yet introduce `androidx` dependencies in the real project.
In addition the sample project contains the [`SaveStatePhotoView`](https://github.com/johnjohndoe/PhotoViewTest/blob/master/app/src/main/java/com/example/testphotoview/SaveStatePhotoView.java) which is responsible for **keeping the state** of the image view such as rotation or zoom level.

The state is successfully restored on Android 9 and Android 7.1.1. However, on Android 6.0.1 the state of the `PhotoView` is lost. I tested this on a Nexus 5. I cannot figure out why - can you spot the reason?