Check that their device shows that the rower finished this piece.
If it does, and there is a cloud icon in the top right corner, the device is having trouble connecting to the network. Check that it’s connected to the best Wi-Fi or its cellular network is on, and then try tapping that cloud icon to upload the piece.
If it doesn’t have the result on the screen, it’s likely something happened that disconnected the device before the rower finished their piece. You can record the result yourself. See the question, “How do I add a piece result manually?”