I connect LED between 15 an 17 and now the LED is always ON when pc is in a sleep mode, so I go back to 15 and 19, there is at least sometimes in OFF state

??

I don't understand this, that must be some bios issues. I must say I'm disappointed with this Gigabyte mobo: XMP doesn't work, slow booting, power LED problem, there is tons of thing in bios to set and no explanation. I would never buy a gigabyte motherboard again !