I have my apple tv 4k hooked up to a Denon receiver using HDMI ARC to an LG 4k TV. When watching a video and pressing either the 10s forward/backwards skip, the audio is delayed by a full second. So what ends up happening is the video seeks instantly and then you see people's mouths moving for a full second before you hear anything. Using the plex client, the video and audio seek instantly and there is no delay in the audio resuming.
In the Apple TV settings, forcing the audio output to Stereo solves this, but obviously is not an ideal solution
Edit: I plugged my Apple tv directly into my TV and bypassed my receiver. I used the internal tv speakers for sound. The delay still exists.