Just something in the hardware chip, but it sounds like it is limited to the 4k/120 hz output. Using the 4k/60hz default output is fine. This will likely only matter more for console gamers.
The workaround is to use eARC from the source to the tv back to the AVR for sound processing instead of the reverse.

I'm wondering how many people will look at this who bought these AVRs recently and might put them up used for sale.
I'm going to start watching the boards for deals.

"Those who preach the myths of audio are ignorant of truth."