If you need to make an update to a class in PeopleSoft, make sure you are not also editing the class in 25Live at the same time. Why? Unfortunately, the update from PeopleSoft will be blocked as 25Live thinks you are in the process of updating the class, and all other attempts to update the class will be blocked.
So, what can you do if this happens? Get out of the class in 25Live and make another small change to the class in PeopleSoft/CCS to trigger the actual update. Example: Add 1 to the enrollment capacity and save. Once you see the update in 25Live, go back into PeopleSoft and change it back to the correct enrollment.