Hi @piggy2008, welcome to the forum 
Can you confirm that your vehicle
- has some form of positioning sensor (which is required for GUIDED mode to operate), and
- works well when controlled in Manual, Depth Hold, and Guided modes via QGroundControl?
I haven’t heard of Rviz before, so have no experience with it. If you provide some more information (vehicle setup and configuration, software and firmware versions in use, any other relevant details) I can ask our software team whether they have some idea what is going on, but if your vehicle is set up correctly for positioning then there may be some kind of issue with your Rviz setup or output, in which case you will likely need to seek help from the Rviz developers.