Multi-Part Series as Audiobooks

After importing m4b files, Apple Books automatically detect that multiple of those are part of the same series and combines them into one for simplicity. But then comes a little problem.

On MacOS everything is fine, all chapters are present. But on iPhone (iOS 26), a few books from the series go missing. On finder I can see that those parts are synced, but for some reason they're impossible to play from the iPhone itself.

After unchecking one existing book, another one takes it place. But not always. Is there maybe some kind of size or length limit?