I've got a dual boot Ubuntu18.04/Win10 system with the BIOS set to 'Legacy Boot'. I can boot fine into this system. However my mkusb live USB (also 18.04 with persistence) won't boot if I leave the BIOS in 'Legacy Boot' mode.
I can swap the BIOS toggle to 'UEFI Boot' and my mkusb live USB will proceed to boot without issue. When I try to boot normally to Ubuntu/Win hard drives the system throws an error along the lines
error: no operating system, and I have to change the BIOS back to 'Legacy Boot'.
What is going on with my system?