I was coming to open the same issue on my RPi4. It's not linked to HD audio but to PCM conversion : Since LibreElec 9.2.1, audio converted to PCM has mixed front channel i.e. center channel is randomly played on left, right or center speaker. Playing the same file several times in a row will get a different front speaker to get the center channel...
Here is a debug file : http://ix.io/2hgx
On this log, I'm playing the same video with eac3 audio 4 times. As I don't allow eac3 passthrough, audio is converted to PCM.
The 2 first plays, center channel were on the right speaker, 3rd play it was on the left (might be left then right, I don't remember for sure but it was not center ) and the 4rth play was the good one with center channel on center speaker.
Juste pausing a video can make the channel to switch speaker.
I reproduced it with eac3 and aac audio.