I have a home built desktop with an Asus Maximus V Gene mob with a Intel 3570k CPU running UEFI on Win 10 Pro 15031 preview. All updates have been applied and I have the latest BIOS from Asus.
I have 3 SSD's, each with a separate OS: (1) Win 7 HP 64 bit (2) Win 10 Pro (upgrade from Win 8.1 Pro) (3) Win 10 Pro 64 bit Insider Preview 15031. I recently reinstalled all 3 OS with the UEFI interface. SSD's are all GPT. All boot and run well.
My concern is when running Win 10 15031 preview I can not boot if the "Secure Boot" (in the BIOS) is in the UEFI mode. When I change to "Other OS" the boot is ok. CSM is in the UEFI mode. When I do attempt to boot with "UEFI" selected in the BIOS I get a black/DOS screen with a message I need to repair my system. There is a message "Error code 0xc0000428" and "The digital sig for this file couldn't be found." I installed and ran the MS tool "Sigverif.exe" and it shows all files ok. Since I am running a beta/preview I do not have a DISM Restore Health available. SFC/ Scannow shows no faults.