FWIW: I've moved this cdrom device to another SATA port on the motherboard so that I could then change the configuration in the BIOS for this port to not use AHCI and the problem has gone.
FWIW: I've moved this cdrom device to another SATA port on the motherboard so that I could then change the configuration in the BIOS for this port to not use AHCI and the problem has gone.