When you call it I hope they review FIRMWARE VERSION and settings but if they don't ask them how to check if the firmware is up to date. They also should have you do a factory reset. Again, follow their instructions. If they can't resolve it, they should offer a service call. If they don't, ask for it.
If they can't resolve this on a new set, you may be looking at a return as defective.
-> ONE LAST THING. Sometimes the handshake is lost or there is an audio encoding problem. For the source that loses audio I always try setting that source to PCM or Stereo to see if the problem vanishes.
I have an LG OLED55C7. I am using 3 HDMI inputs that include: Directv, Apple TV, and a Sony Blu-Ray player. All has been fine for months. Now when switching inputs I lose audio to the input I've gone to and previous input. No audio through internal speakers and Yamaha Sound Bar. If I make a few more input changes. Audio comes back. Also, if I use TV's soundest, audio will return. I've switched cables between Apple TV and Blu-Ray player and still lose audio. Thanks for the advice!