Thanks a lot for the logs!
If you have to use hdmi_force_hotplug on the RPi then I suspect the hotplug-detect signal might be indeed the culprit and the soundbar doesn't detect the TV because of that.
When directly connected the RPi got a valid edid from the TV, indicating 1920x1080p60 as preferred mode.
The edid from the soundbar looks like it sent a fallback safe-mode one - preferred mode is 1280x720p60 and the 24Hz mode from your TV are missing. But AC3, DTS and multi-channel audio support is listed.
The hotplug detect issue could be caused by the cable (hotplug not wired up or cable broken) or it could also be caused by your TV "misbehaving". Both of that happened to others before, too.
Using a different HDMI cable and/or HDMI port on your TV would be the easiest thing to try. Other than that I'm out of ideas - if the TV and soundbar don't play well together because of the TV's hotplug issue I'm not sure there's anything easy you could do about it.
so long,
Hias