Okay, being honest I'm getting better at installing and understanding arch instalations, but i still need your patience. I've been suffering with the same problem. After following wiki step by step and installing GRUB, I umount /mnt like it says in wiki, rebooted in terminal, and took off my pendrive. It failed (yes, the grub was installed correctly and I verified, even in pacstrap)
I entered in EFI Shell, and found grubx86.efi in FS1:\efi\EFI\GRUB\grubx86.efi.
Then, I typed grubx86.efi to initialize it, but it rebooted my pc and come back to my BIOS, where through secure boot control is off, and the device priority only shows my pendrive.
I'm pretty sure that my configs instalations are right, but what it might be the problem?