Similar issue, same setup (Odroid C2, latest LibreELEC), except that in my case I'm having problems specifically with aac/mp4 files.
Aac/mp4 videos play without sound. Aac/mp4 audio files (music) play without sound.
Other formats, stereo or not, work fine.
Anyway, so far, I've found 3 workarounds, but none of them is ideal.
1-Play everything through the default/analog output. This doesn't affect passthrough signals, but plays music files through Odroid's DAC, which sounds considerably worse than my AVR's DAC.
2-Enable "stereo upmix". This makes aac/mp4 play, but will upmix everything that doesn't passthrough, including my music files. Far from ideal, in fact, I'm yet to find any upmixing process that sounds good.
3-Enable "stereo upmix", reduce number of channels to 2, enable "Dolby Digital Transcoding". When you reduce the number of channels to 2, a new option called "Enable Dolby Digital Transcoding" shows up under "Passtrough" settings. This allows video files encoded with aac/pm4 to be properly decoded by the AVR...Again, the downside is that music files are still processed by Kodi; They're not really upsampled, since there are just 2 channels selected, but are still being unpleasantly processed.
To sum up, the problem boils down to playing music. Every one of the above workarounds "solves" the "video without sound" issue, specially option 3. However, in every one of them music quality is still being affected either by Odroid's DAC or Kodi internal processing.
If you ask me, this is a bug.
log: hastebin