1. The sections that are included in the report come from the setting in the corridor Design Stages. If you look at the properties for the Design Stage, there is a section to Include Critical Sections which will have some values set to true. If you wish to only include the interval you must turn of all these options by setting them to false or changing the design stage in the corridor properties to a stage which doesn't include these critical sections.
2. The answer to the second part is related to the first answer. The sections that will be included are those that are drops in the corridor. The volumes report will run each time you open the command and to get end area volumes it is required to have more than one section. This is because it must have an interval it can use to compute the volumes, otherwise you will just get areas of components.