VLC on Android isn't a good choice for playing audiobooks. It loses a few seconds when trying to change playback speed. Also, it doesn't understand a folder of audio files as one book.
I switched to AudioAnchor from F-Droid. It doesn't suffer from the above two issues. However, it expects a folder for each book, even if it's a single file.
I have a Syncthing folder for Audiobooks now, holding only the current ones.
Peter Vágner likes this.