You sure it's not booting kernel from eMMC, and the rest of the userland stored on NVMe? Admittedly it's been a while since I looked into this, but this was the closes solution available at that point. I'd like to get rid of the eMMC module entirely so the setup truly is "NVMe only" without having to keep the eMMC module around just for initrd and the kernel. Supposedly they can boot from the internal SPI flash somehow, and then "jump" to NVMe, but I don't know how.