Amazon Fire TV Stick 4K Max Black Screen
To my regret sometimes when playing so called Dolby Vision Profile 7 MKV files, the screen turns black. When playing the same files on an LG C8, via the Emby App. It plays fine in HDR10.
I've been part of the threads on github reporting these issues. The key issue is HDR10PLUS and DV - simply does not work unless you strip the HDR10PLUS metadata, leaving just HDR10. HDR10 and DV (to make DV8) DOES work just fine however, but the 4K Max seems to be very strict on the format. I've found remuxing/correcting with the dovi scripts from RESET_999 does the trick, and I have 100% success rate here.
This is with the standard AndroidTV/FireTV Emby client - it works just fine.