Microchip's Support page.Microchip's Contact page.
As part of Part marking change due to the migration from Atmel to Microchip, the package identifier has been removed from the device marking as this can be observed visually for different packages. This will be updated in the upcoming revisions of the device datasheet. As per this new marking the ATMEGA328P U are valid devices without any process change. Please provide more details on the application and nature of failure so that we can check this further.