Hi Paulo A, was this case ever resolved? I am having the same problem. I have created learning activities that require different audio files to be played on the same page as part of different events.
For example, drag a word to the corresponding picture (3 words, 3 pictures). The audio file 'try-again.mp3' is used for 3 different events; whenever any of the words are dragged outside their nominated drop zone. Likewise, the audio file 'well-done.mp3' is used for 3 different events; whenever any of the words are dragged to their nominated drop zone.
I get duplicate object errors when exporting to epub3 file, but when I export anyway and check, the page works as intended. I can upload to Kobo (although they give me a warning about the error) but iTunes Producer will not let me upload.