Maybe some driver alias does not match anymore. Could be check with:
apt install pciutils
lspci
This print a list of PCI devices with some bus address. With the ID of the eMMC, check
cat /sys/bus/pci/devices/0000:<address>/modalias
And with the returned alias check
modprobe -R <alias>
If it prints an error, it means no driver matches the alias of this device.
We could check whether the device alias changed between the Linux version (unlikely), or whether the driver does not expose/support that alias anymore (more likely).