LOL 3 years later I'm seeing the exact same thing with a Sony Bravia when enabling the "enhanced HDR".

ChromeCast ultra => 976 => Philips Hue Sync => Bravia TV.

The video randomly blinks in and out.

I I take the 976 out of the chain the video is perfect (and indeed the image is better than without the enhanced HDR)

ChromeCast ultra => Philips Hue Sync => Bravia TV.

If you still read this post, did you find a solution?
I'm thinking of moving the 976 as a pure sound system like:

ChromeCast ultra => Philips Hue Sync => Bravia TV => 976 through ARC