Apple TV 4K occasional failure or delay in starting soundbar's sound at start of program

When I start a new show, my Polk Magnifi soundbar sometimes does not produce any sound for anything up to a few seconds to a few minutes. (I would guess it would never start in the "few minutes" case, but that's as long as I've waited.) In the cases where it does start the sound, the orange light at the front of the soundbar turns green. (Manual says that means "Dolby Content", but I'm guessing it means in this case that syncing has completed.)

All components and cables are new. The HDMI cables are suitable for 4K. The Apple TV was bought last. Prior to that, the TV and soundbar were connected and they worked fine. TV is a Samsung QLED model.

The Apple TV has a hardwired ethernet connection to the router.

The connection to the soundbar is to HDMI 1. (Belkin Ultra 4K cable, Apple's recommended one.)

The connection leaves from soundbar's TV(ARC) HDMI port, via the cable supplied with the soundbar.

It connects to the TV's eARC port.

This happens maybe once per five starts. When I give up, leaving and restarting the program will usually – but not always – result in the sound starting within a second.

There is very frequently 1-3 short dropouts at the start of a program, whether or not the sound started immediately. I've seen that issue in posts dating back years, but I haven't found a post about this long delay.