Apple TV to S50pro Via Samsung TV

I Connected to the S50pro with fiber optics from a Samsung The Frame TV and this to Apple TV 4K via HDMI. From the S50pro + I connect through the RCA output to a Kenwood Tuner, model UD70 (A522). The sound setting of the TV is by bit rate instead of PCM and the Apple TV is ALAC.
When I play music on Apple Music from Apple TV, it starts up fine, but after a couple of seconds it decreases the volume for about 4 seconds and then normalizes. Will they have corrected this problem with some new firmware?. In 4stream no new updates appear.

So the connection is ‘Apple TV’ --(HDMI)–> ‘Samsung TV’ --(OPTICAL)–> ‘S50PRO+’ --(RCA)–> UD70, right?
The OPTICAL and RCA is single way, so if the volume changes, the most likely reason is the CEC messages between Apple TV and Samsung TV. The S50PRO+ in the end can’t do anything.

ok, thanks for the explanation.