“Data has changed” means that you have changed some parameters of a strategy – for example the look-back period. To save the changed parameters you have to click the “Update” button. The “Revert” button will always go back to the saved parameters. For example you can optimize or change manually a parameter and look at the result using the “Apply” button. Now if you don’t like the result you click on “Revert” to go back to the saved version. If you have changed some parameters and did not save them with the “Update” button, then you will get the “Data has changed and will be lost if you continue” message if you change to another strategy because your changes will not be saved.