Hi, I have the GL12CP as well, I found this thread searching for any issues with a 2nd HDD.
I've already been burnt by the "4 DIMM slots" deception by Best Buy (there ARE 4, but you can only use 2 at a time because of the crippled intel H.310 chipset) so I wanted to know first before spending good money for something useless.
According to ASUS the "CP" only supports 4 SATA ports (CX and CM have 5, intel Z390/Z370 chipset); one is the SSD (since CP doesn't support PCIe it's an M2 SATA model), one is the 1TB HDD, one is the Optical drive and the last one (presumably) is the swappable bay.
So it looks like that's what the problem is.
Apparently the missing SATA port is located under the graphics card, but the chipset is not supporting it, so I'd have to consider to not use the hot-swapable bay?
