Hi,

Do you have any idea about how he customized the report format ? If it is via a custom module, check whether the module is still installed in the database. If he directly edited the original views from the user interface, it will get lost, once you upgrade that module.

If he created custom inherited views, make sure that those views are still active in the db. In order to check it, activate the developer mode and navigate to Views menu under Settings menu, and filter the qweb views and filter inactive/archived records from search view and see.

Thanks & Regards

Walnut Software Solution