If using the system WinUSB INF file (not a device-specific INF) the GUID in the device firmware must match the GUID in the application you use to access the device.
My firmware and application use the same GUID, but it's a different GUID than the Microchip firmware and application uses. So if you want to use my firmware and the Microchip PC application, you need to change one of the GUIDs or provide a device-specific INF file.