I am having the same issue. video aborts while playing from a crucial ssd on a usb hub connected to my Roku Ultra.
I tried replacing the Roku with a new Roku, but the new Roku only recognizes 1 drive on the USB Hub.
For video playback issues, you need to provide some additional information. We need to know the container of the media (MKV, MP4, MOV, etc.), and the video and audio codec within the container. It doesn't tell us anything if you say your media is a MKV or MP4 file. The codec information is critical to help troubleshoot.
How do you find that information out? There are several ways to get it. One is to use an app on a computer that can read the file and provide the information. One such program is called MediaInfo. It's free and can be installed on Windows, Mac or Linux computers. A simple command line program is called FFMPEG, but if you're not very computer savvy I don't recommend using any command line program. Also, media players such as VLC can provide the media information, and it too is a free program you can install on your computer.
Just be aware that Roku has not made any meaningful updates to RMP for over three years. It has some bugs, and until Roku decides to put some effort back into the program you are much better off using a computer based server like Plex or Emby. There's one or two other Roku apps/channels that can play media from the USB drive, but none are free and I have no experience with any of them. I did have experience with Chaneru many years ago, but that developer seems to have lost interest in it, and it doesn't work well at all anymore.
