HDD not recognized GPT UEFI

Hello,
I've got an Asrock Fatal1tyZ68 Professional Gen3 Mainboard. Before I had Windows 8.1 installed on a small 512GB HDD with MBR and everything worked fine. Now I've switched to a 6TB HDD. The Problem is I had to switch to GPT because of the size.

The strange thing now is. When I unplug and replug the HDD it is recognized as a bootable UEFI option. When I restart it is not recognized as an UEFI option anymore. When I try to boot the HDD without the UEFI option I only get "please select a bootable device".

The workaround can't be that I have to unplug the HDD everytime I need to restart!?

What can I do?

if you can disable legacy support via the bios...
set drive controller as AHCI

see if that helps

No there is no way to do that.

Drives already set to AHCI.

was this a clean install to the New 6tb drive ??