The MCUXpresso SDK USB Stack Composite Device User's Guide, section 4.2, says the config list count should be the number of classes in the composite device. It shows as example MSD+CDC is 2 classes.
Shouldn't CDC+CDC be 1 class? The SDK example twrk22f120m_dev_composite_cdc_vcom_cdc_vcom_freertos shows it as 2.
CDC+CDC is two classes, usb stack will need allocate more memory. You can consider it as the count of classes rather than the type of classes.