I am having the same issue with the Mezzmo app on Fire TV and Fire TV stick (both latest versions), except the files I am having issues with are .mp4 files. The files are ripped from my DVD and BD collection using makeMKV then converted to .mp4 using Handbrake. Typically the file sizes are between 2GB and 6GB. During panning scenes the video becomes jittery, but is fine on static scenes. Like the original poster, the files seem to play fine on other media players/devices.