Comment 107 for bug 1359689

Adding my experience in case someone has the same issue.

Installed a fresh Ubuntu 16.04.3 with the clear entire drive and set up LUKS+LVM option. After the first reboot I got the graphical password prompt but couldn't type anything. After the next reboot, after passing GRUB, the screen just stayed blank purple. Only ctrl+alt+del worked.

To get the system boot correctly I edited the default GRUB Ubuntu entry (the 'e' key in GRUB):

1. change the line "gfxmode $linux_gfx_mode" to "gfxmode auto", or just remove it whole
2. remove the "splash" from the linux kernel cmdline
3. boot with F10

After that I got a text prompt to unlock my disk volume and after giving it the password the system started normally.

If this works for you and you want to make it persistent, edit the /etc/default/grub file (with sudo):

1. remove the "splash" from GRUB_CMDLINE_LINUX_DEFAULT
2. uncomment the line GRUB_GFXMODE and set it to "auto", GRUB_GFXMODE=auto
3. save the file and run the command "update-grub"

Hope this helps.