What I did is the following:
- I removed all files on the ssd partition
- cloned the emmc with the script from rootonnvme
- Installed the chroot service
- Tested that this system was working properly
- I removed the setssdroot service from the ssd
- I changed the fstab on the ssd to
/dev/nvme0n1p1 / ext4 defaults,errors=remount-ro,discard 0 1
- rebooted
Reading your post richg, I have to say that I cannot exclude atm that the emmc was mounted first and then the setssdroot service from the emmc chroots…