It looks like this problem has been well-known for a few years now, but no firmware fix from Roku to keep from trying to Dolby Vision transcode rec 709 material in MKV containers when being sent to 1080p display devices.
https://community.roku.com/t5/Channels-viewing/Severe-color-contrast-distortion-while-Plex-streaming...
I reached out to online chat and phone support yesterday, but spent two hours having people tell me to reset my Roku and try again - beyond worthless.
