When you have several versions, customers over time migrate to your latest version. Later versions often contain more functionality or changed functionality. The customer often expects that what he could do in the old version is possible in the new version as well. A very logical expectation. One you need to deal with.
It is quite common that functionality changed and requires a different set up to get the same result. This requires a change at the customer site. And change is often not wanted by your customer. He wants what he was used to and demands to have it corrected. Of course that is not possible because we are talking about a different version of the product. So here a good discussion with the customer is required to get a clear view on his arguments why not to change.Based on your company policy you know which customer arguments will lead to a change made by maintenance. Follow up on it. Stand up for the product. The newer version brought the customer more else he wouldn't have migrated to it. Changes are involved. The customer has to digest those. Help him setting up the functionality to get the result he wants.