Interesting, I’ve tried both files and they correctly switch to Dolby Vision on my TV. 
I will need to look over the logs from a Dolby Vision playback attempt, it should hopefully highlight why the Dolby Vision mode isn’t working correctly. Steps on grabbing the logs are available here: https://support.plex.tv/articles/201573117-android-android-tv-fire-tv-logs/
Here’s an LG Dolby Vision sample that is single layer and uses MPEGTS as a container, if you could give this a try and let me know how it plays that would be great. https://drive.google.com/file/d/1kKRoJEgsDeE59Nbuy8A1DsSvc3eBac08/view?usp=sharing
With this video, an easy way to tell if it’s Dolby Vision will be when the sea scene comes on with the boat (10 seconds into the video), without Dolby Vision the sea will be green, with Dolby Vision it will be blue.
Without Dolby Vision:
With Dolby Vision:
