You seem to have a hardware issue, If you don' t want to RMA or return to Vendor if your in return period? suggest you get a
Right Hand USB 3.0 Extender cable and a
USB 3.0 Hub. Run your External drives from the right side ports. I have good luck with the link devices I can run up to 3 2.5" external hard drives at the same time and a USB 3.0 thumb drive. Seem is I try 4 external drives I have problems with dropping off with all 4. I'm sure this is a Power to the port problem. With USB 3.0 Maximum power from the port is required to the Hub for full power. The Right hand forward port has extra power going to it for Charging Cell Phone, Tablets etc. That's the one I use for my external drives.
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro