The Student/Educational version has a licensing restriction in the music/sound encoder for the MP4 format.  

As such Lumion needs to render your Movie or Clip using MP2 and not the normal MP3 sound encoder for MP4 videos.
 
If the video player on your PC does not support MP2 playback, then the sound will not be heard.

The Commercial and Trial versions are not affected by this restriction.

These PC media players are not playing the MP2 track, as of August 2024:

• Windows Films & TV.
• Windows Media Player (including legacy player).

Your video sound/music should play correctly with VLC.