This query relates to the information entered in the class details area of the census. To check and amend this go to Admin > Census > Spring > Class Details. In this area you are looking at the details for classes that show at the top of the page.
It is expected that you have class details added for each year group between the lowest and highest year group recorded in Admin > Config > Core Setup > School.
If this information is not correct you can click edit above the table, amend this and click update at the bottom to save.
To add the missing class details go to Admin > Census > Spring > Class Details > Add new. Fill out all the details and click add.