In LibreELEC go into Settings / Player > On the 'Videos' panel scroll down find "Adjust display refresh rate" to On start / stop
found fix here it's the last post on this thread down very bottom
It does not work for me. Still no sound after wake-up. However I found a very dirty solution by a small script which enters then exists system settings window.
This is the code
#!/bin/sh
case "$1" in
pre)
# <do something on suspend>
;;
post)
# <do something on resume>
sleep 5
kodi-send --action="activatewindow(Systemsettings)"
sleep 1
kodi-send --action="back"
;;
esac
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It has to be put into /storage/.config/sleep.d folder
With these copmmands the folder and executable file can be created
mkdir -p /storage/.config/sleep.d
cd /storage/.config/sleep.d
touch 01-make-sound
chmod +x 01-make-sound
Edit the file and copy the content above with this command
nano 01-make-sound