Voiceover/Background Music and Changing Any Video in .Key File

In the latest version of Keynote (11.2) I've noticed two behaviors 
that didn't happen in previous versions. After placing the images, 
transitions and at last recording narration (voiceover). 
If we increase or decrease the background music it randomly 
disappears from the final exportation in video.
2.After recording the audio (voiceover) if we want to change 
some video (.mp4) from the final .key file, it will not be 
possible to edit it, leaving the frame blank.