Yup, you and everybody else with slow internet (including me) gets that same message when trying to download 4K from the internet.
Sad, but very true. Yup, our internet is slow by today's standards (5-6Mbs at best, 3Mbs average typical). Just seems odd that we get that error being it's not streaming video but downloading a file. Also, I know H.264 4k files can be quite large but the H3 is also H.265 compatible which makes 4k file size more like HD H.264's size.
In any case, Dish must know that the majority of their clients live in places where internet (if any) is slow. Maybe it's just an H3 bug(?).
BTW - the Channel 1 pre-loaded VOD is a great idea! Just need better selection of 4k movies. Still early but they're coming!