You may have a poor network connection.

Mobile Voice needs a strong network connection to work at the top of its game. Here are some things you can try:

1. If you're using a Wi-Fi connection, turn off the Wi-Fi on your device and rely on cellular data instead. The Wi-Fi may be jumping around and searching for a connection, so try to use cellular data when this happens.
2. Move to an area with a stronger cellular connection. If there’s nothing immediately close by, a nice quiet parking lot may be just what you’re looking for after a visit!
3. Jot down a few keywords in your notes that will prompt you to continue a more detailed narrative later, when your connection is better. Dictating the majority of your notes will still be faster than typing.

For more information, see Mobile Voice Poor Network Connection Error