I too was quite happy with Channels when in HDR mode - I found the “HDR Bright” mode on my LG to be fine, with the only issue being the weird flipping between dull/bright video when progress bar or quick guide overlays came up over video.
The annoying issue with video flipping suddenly between dull and bright for overlays was actually fixed in one of the early tvOS 11.2 Beta versions (think it was Beta 2) and that Apple fix ironically appeared a day or so before Channels was updated to cause a forced switch to SDR mode.
I too was surprised when Channels kept switching to SDR when I’d set the ATV’s Video settings to not auto-switch between HDR/SDR. Not sure if this is a flaw in Apple’s implementation of this new feature or an intentional override by Channels?
If the Channels switch to SDR is always going to be forced, I’d much prefer a setting within Channels to enable or disabled the forced switching. I understand the reasoning behind the switching, but it clashes with the preferences Apple have given now in 11.2, with which I prefer not to allow HDR switching due to being happy with the HDR and more annoyed by the delay the switching introduces as the HDMI re-negotiates on starting/exiting the app.
