I installed Ubuntu 16.04 in an Acer R5-571T 59DC notebook for dual booting with the preinstalled Win 10 (UEFI).
After restart there is no GRUB menu and the PC boots directly on Windows.
I disabled secure boot and fast boot before install, and also used "boot repair" with a live usb. No luck.
I managed to start Ubuntu using Super Grub2 Disk, so I think GRUB is ok but without the super grub pendrive I cannot boot Ubuntu.