I'm posting to report a bug that seems to occur on rare occasions. Every once in a while my Surface Pro 6 gets stuck at 0.40GHz while it's plugged to the adapter but works fine on battery. I've had this issue occur about 4-5 times throughout the 6 months I've owned it. The only fix for this issue is re-installing the Surface Pro 6 firmware. I think it's more firmware related than hardware, or maybe the chip that holds the firmware is defective? Anyways, I thought I'd report this issue because it still needs fixing.