Steps to turn Google Classroom Auto Sync back on:
Navigate to the Don Johnston tools website.
Login to the website.
Select Manage Students.
Select Google Classroom Classes.
Click on the Enable Auto Refresh Button. (two arrows in a circle with a diagonal line)
Click on, "Enable".
Click on, "Proceed".
Follow Google's steps to log into your account.
Click on Allow.
Check Notify me, if you want to know when the sync is complete.
Click on, "OK".