Amazon Firestick 4k and Dolby Vision

[ragico 11]

I did a few DV mp4 single layer using Dvd Fab with ac3 soundtrack.
I played them using the amazon firestick 4k and emby app for this device. Emby server running on my nas.
Some of these mp4 play normally, others (like spiderman homecoming, The Secret Life of Pets 2 , Game of Thrones seasons 1 and 8 etc) play only audio and black screen. Tv used Panasonic gx serie.
Then I tested the firestick 4k on Lg C8 and had same results.
Therefore I think that the firestick 4K for some unknown (to me) reason do not reproduce video from all the DV mp4 single layer, but just some of them.

Anyone knows why?