I am facing to this issue across several LE versions (from 9.2.6 to 11 Nightly) and more or less it's still the same or similar behavior.
It usually happens when the DVB-T2 signal level / quality is not perfect but sometimes also right after switching the channel, even though the DVB-T2 signal is excellent. Then the Audio is lost (which means muted, it happens randomly, when the DVB-T2 signal drops for a moment or after switching to another channel and it takes an unpredictely long time to recover).
When playing recording of the same stream, the audio is restored quickly but it does not happen with the live stream. Usually I need to switch to another channel (but then the TimeShift data is lost which is very annoying), sometimes it helps toggling audio stream (where there are more than one, which is not always).
The current configuration is RPi 4B/2GB, LE 11 Nightly 20211108
An example video recording:
Debug log while LiveTV watching the same stream as the recording above (got back with TimeShift, activated Debug log before Audio was lost, deactivated Debug log when the Audio was back again):
The question is why there's a difference between LiveTV watching and recording play and if this can be improved (to recover audio quickly after stream corruption during LiveTV watching).
BTW. as already reported in another thread, subtitles on this channel are not visible during LiveTV despite recorded properly and visible when playing recording ( this is an incompatibility of Kodi with Tvheadend 4.3 backend).