Sometimes, VESA buffer cannot properly auto-detect the resolution of your screen during boot-up. You may set the VGA/VESA resolution there using grub. To fix it, open /etc/default/grub in an editor

# Adjust the following lines:
# see also https://askubuntu.com/a/609523
# GRUB_GFXMODE=1280x1024x32
# GRUB_GFXPAYLOAD_LINUX=keep

sudo update-grub