If the class you have been using with your students this semester suddenly disappeared, you can probably find it under "Past Classes" on your teacher dashboard.
Earlier this year we made some changes to the way classes are grouped and displayed on the teacher's dashboard. So if you have classes that are ongoing, but have an end date in the past, those are now hidden under "Past Classes." You will need to look for the class there. Click the three dot menu on the class to edit the class and change the end date to a future date when the class will actually end. That should move the class up to the "My Classes" section of the dashboard.