One thing I can say is that I only have this issue when watching cable/TV. When I play Playstation or plug a USB in to watch a movie I do not have the sound issue.
I don't think its an issues specific to the TV since I am using a Sony TV with LG soundbar. Have you tried connecting the HDMI to HDMI for sound? Maybe its just an optical cable issue with LG devices?
I have a new Sony TV and new LG Soundbar. I have the intermittent cut outs with my soundbar as well. I am using an optical cable so I do not think its a connectivity issue. Not sure what else to do.