Well... the little I played with full disk encryption it should make a separate /boot partition so FDE isn't needed with grub, the boot menu. Sanity check, it says GRUB and its version on the screen?
I've seen the grub menu AND the Advanced options menu render only partially. Escape the Advanced menu, re-enter may straighten it out. Just a guess on my part.
Immediately after starting boot, after GRUB, is when it should ask for the FDE password, I believe.
EDIT: Here's GRUB and the Advanced options menu.
Don't let the mouse cursor fool you - GRUB is keyboard only.