Hi,
I posted this last night but put it in the add on support thread by accident 
I have been using libreelec matrix on my pi 3b for a little while, running it over composite out on one of my old school TVs.
I have some content that is encoded hevc 265 which is not supported by libreelec matrix on 3b due to the pi's lack of hardware decoding. as recommended, i installed 9.2.8 to use instead so I could play my content
But here's where it gets odd! Upon booting I found that there was some very strange crackly sounds being output. I checked the audio device that was listed as HDMI and switched it to analog. I then went and tried to play some of my h265 content, and the audio was pitched way lower than it should be. I also noticed that moving the mouse was extremely laggy, like the fps was low, however the video playing looked fine.
Guessing that my 3b was just struggling to decode the h265, I tried a different video that I know worked perfectly on matrix. This had the same issue. ALL my videos had this same issue.
And the weirdest part is the audio is perfectly fine over hdmi, although the mouse lag issue persists.. I tried using the HDMI and analog option in the menu, but this didn't work either and just caused weird broken audio to play.
Anyone got any clue what the problem is here?