When upgrading Acumatica, if a native feature is being replaced with another feature, then the expected behavior would be that these features continue to work after the upgrade with little or ideally no user intervention. This is not the case, and has happened more than once during an upgrade.
An example of this is the new Labor Cost Rates screen that was added. This replaced the employee rates that were entered on the Employee screen. We use project accounting heavily, and after upgrading, we had to manually re-enter all of this information. All of the data was lost after the upgrade. Luckily, we upgraded our sandbox first and tested and realized the problem. We still had to figure out how to manually export the data from the old version and import into the new version. This is very frustrating.