Getting "No such device xxxx...." at boot but the device *does* exist

[Chris Green]

I have added a new ubuntu 19.10 installation to my existing ubuntu
19.04 system.  The 19.10 is installed on an NVME SSD.

I have run os-prober which identifies the new 19.10 istallation
correctly and I've run update-grub to add it.

At boot I get the expected menu offering 19.04 as the default and
19.10 as a selectable option.  However if I try and boot 19.10 it
fails with an error:-

    error: no such device: c6ca1c2d-4837-48b9-8fa6-1ef47251d7b7

Fortunately it then just drops me back to the boot menu so I can boot
19.04.  However the device c6ca1c2d-4837-48b9-8fa6-1ef47251d7b7 does
exist, it's the correct UUID for the 19.10 disk drive.  So why doesn't
19.10 boot?

Is it possibly that the boot can't "see" the NVME disk drive?  Does it
depend on the BIOS to read the disk at this stage?

-- 
Chris Green