Make sure the Roku TV screen mirroring settings are set to Prompt (not Always Allow) and if/when prompted, then choose "Always Allow" for the specific device.
Try restarting both the Roku TV (using the Restart option in Settings) and the NordicTrack (dont know its menu).
Otherwise, try switching the WiFi connection to either/both the TV/Track to 5Ghz if at 2.4Ghz, or 2.4Ghz if at 5Ghz.