It is Svit - Project Gutenberg Ebook Reader. It uses books folder (that should exist). It works for anybody except for one customer that switched a device (on older one it worked fine).
On initial run the app copies ebooks from app folder into books shared folder.
On my device it works fine.
Additional info:
At start-up I use shared-object. Can it be corrupted if backup-restore was used while switching to the other device? But reinstall should delete all those objects (proof: EULA is shown again after reinstall) so the problem should be eliminated on reinstall. But it is not!
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