Viewing the Classes page after adding sections to students or using the Copy Scheduling Results to SEC/MST, you may encounter the sections missing from the page.
Please find the View Only Current Term check box at the bottom of the Page and deselect that option.
This would be caused by the Terms of your school not including the date displayed by your computer.
Deselecting that option will allow you to view the classes no matter the Term dates versus your computer date.