UEFI fails on Dell PowerEdge R710

I have tried two different Linux-based hypervisors - PVE and XenServer - and they fail in the exact same way.

After installation, when the machine boots into Grub, Grub cannot find the OS. Doing an "ls" shows that it sees (hd0) but cannot load its GPT at all - it says "unknown filesystem". Doing an "insmod part_gpt" does not help. Installing and booting in BIOS mode works fine.

What is going wrong with UEFI here?