Thanks for the note.
While we don't typically recommend using mobile hotspot connections for streaming, I'd like to gather a few more details here to see what may be causing the issue. Please PM me with your Roku account email address, the serial number of your device from Settings>System>About, and the version of iOS that your device currently has installed. Feel free to include any other details or steps you've attempted to try an resolve the issue. I'll follow up directly from there to see how else we can help.
Roku Community Manager