This probably means your calendar is not updated. Click on “Calendar” on the top bar and make sure you have availability for the dates you actually need people. You can close availability for the dates you do not need volunteers by clicking on “Edit Availability”. Then you will be able to select the time periods for which you do not want to receive volunteers. They will be closed and volunteers won’t be able to apply for those dates.
If you are receiving applications too far in the future, you can close the availability of those months, in order to gather applications for the near future. Have in mind volunteers can apply up to 6 months in advance.