The Roku media play has a certain amount of video it needs to buffer to play.
If it can’t get enough good data in the correct amount of time it barfs.
And not all media players are the same. I suspect the Roku media plays was designed for local SD cards.
My Roku 3 media player struggles with my hdhomerun. And even my ultra does. And if they are going to barf it’s at around 20-30 seconds.
But the hdhomerun app has no problems.