Apple TV — 5.1 audio channels duplicated in front speakers

I ran 5.1 audio tests on YouTube and Apple Music and noticed that sounds intended for the rear channels are also duplicated in the front left and right speakers. Also, the sound from the center channel is duplicated in the left and right front speakers.

I am absolutely certain that the problem is related to Apple TV because when I play the same content directly through my Android TV's, the channel distribution is correct and everything sounds as expected.

Everything used to work fine, so I believe this is a software issue. I am currently using tvOS 26.1, but I have also encountered the same issue on stable tvOS 18.5 and above

I have already tried resetting Apple TV to factory settings, updating to the latest version, and switching audio output formats, including forcing Dolby Atmos 5.1, but none of these actions helped. (I tried different settings on the TV, but as I wrote earlier, the problem is with Apple TV itself).

Most of the forum posts I found are about Dolby Atmos not working at all. In my case, it technically works, but it doesn't sound as it should.

Connection diagram:

Apple TV 4K (A2843) > TV (Philips, 50PUS7303/RU) > Samsung Home Theater via HDMI ([HTS]J5500K)