Comment 27 for bug 1734147

Are the machines dual installed with Windows 10?
Has there been a recent upgrade to Fall Creators Update? Note that many Lenovo machines fail to boot or boot to black screen after such an update. Such an upgrade affects subsequent boots to both win10 and ubuntu.
Can you get into one-key recovery mode?
Can you get to the boot options menu?
Can you get to the bios settings menu?
Can you configure boot entries in the bios settings to boot from the /EFI/BOOTX64.EFI? SHIM? UBUNTU/GRUB2.EFI?
Have you applied all the Lenovo bios/firmware upgrades?