What EDID setting are you using?
What device are you using downstream of the Ezcoo to digitize the signal?
Does you TV remain/recognize the full 4K Dolby Vision signal from your input?
Unfortunately the Ezcoo is not the perfect solution.
I've found that after using it a while, it works very well with my Apple TV with full 4k Dolby Vision and Dolby Atmos. For me this is good enough as my Apple TV is main media source 99% of the time. Colors were a little washed out, but Hyperion 2.0.14 and newer allow you to compensate for this: from the changelog (New color processing settings: Saturation gain and brightness/value gain. They allow compensating washed out HDR colors on LEDs).
However, when I go to use my Nvidia Shield any 4k Dolby Vision movie that I play though Plex will display a mostly purple picture. The only way I've found to avoid this is to go into the settings and turn off Dolby Vision and force HDR10.
Not sure why it works fine for Dolby Vision on the Apple TV and not another source like the Nvidia Shield. I'm using the
4K7.1EDID setting, downscaling turned on with my Apple TV. I'm just using a generic USB HDMI capture device connected to a Raspberry Pi downstream. I wish there was a USB HDMI capture card/device that could do Dolby VIsion as that would solve all of our issues.