If you're still having this issue you might want to try changing the HDMI Audio Format to "Pass Through" that's the equivalent of bitstream so it should send the audio as intended to a soundbar/AVR. Also it might be worth changing the "HDMI auto setting" to mode 2 in the setup menu. That drops the HDMI port back to HDMI 2.0 instead of 2.1 meaning you lose the gaming features e.g. VRR, 4k120fps but it seemed to fix my audio issues.
Annoying though because I want to use the gaming features. Fingers crossed for this firmware fix.
I also get audio dropouts when watching cable. My TV is connected via HDMI 2 to the AVR's HDMI ARC port. Note that I get cable using the DVB-C tuner and a CAM module in the CI slot. So I am not utilizing any HDMI to get the signal.