There is no firmware downgrade, only upgrade. The firmware or software version of the Utility won’t affect its connection rate, especially if it works fine on another system. The issue would be due to your system. You can always try other ports or a cable.
Vendor Name: G-Technology
Device Name: G-SPEED Studio XL
Vendor ID: 0xC
Device ID: 0x80
Device Revision: 0x1
UID: 0x000C800000008590
Route String: 3
Firmware Version: 25.1
Port (Upstream):
Status: Device connected
Link Status: 0x2
Speed: Up to 20 Gb/s x1
Current Link Width: 0x2
Cable Firmware Version: 0.1.24
Link Controller Firmware Version: 0.14.0
Port:
Status: No device connected
Link Status: 0x7
Speed: Up to 20 Gb/s x1
Current Link Width: 0x1
Link Controller Firmware Version: 0.14.0
If you have the TB2 model and are using 10.12 you want to install this: XL TB2
That version of the GSU is for the older units only and with TB2. So make sure you uninstall your current version and install that one only and see if it helps.
If there are bad drives listed then the best option would be to redo the entire RAID system but yes you can always call in for support. 888.426.5214 for US based support.