Lacie 5bigs not mounting

I've done all that basic stuff on the phone with Apple Support. See below from the system report. It shows that the Mac knows there's 2 daisy chained 5-bigs into one of the thunderbolt ports. But they don't show up in Disk Utilitities, the finder, or on my desktop.

Thunderbolt Bus:

Vendor Name: Apple Inc.

Device Name: iMac

UID: 0x0001000A18166200

Route String: 0

Firmware Version: 22.1

Domain UUID: 49E33E73-ECDA-BF50-A5E6-F1C790542387

Port:

Status: No device connected

Link Status: 0x7

Speed: Up to 10 Gb/s x2

Receptacle: 1

Port Micro Firmware Version: 2.1.3

Port:

Status: Device connected

Link Status: 0x2

Speed: Up to 10 Gb/s x2

Receptacle: 2

Port Micro Firmware Version: 2.1.3

Cable Firmware Version: 1.1.0

5big Thunderbolt 2:

Vendor Name: LaCie

Device Name: 5big Thunderbolt 2

Vendor ID: 0x3

Device ID: 0xA

Device Revision: 0x3

UID: 0x000300005218CF10

Route String: 3

Firmware Version: 24.1

Port (Upstream):

Status: Device connected

Link Status: 0x2

Speed: Up to 10 Gb/s x2

Current Link Width: 0x1

Cable Firmware Version: 1.1.0

Link Controller Firmware Version: 0.14.0

Port:

Status: Device connected

Link Status: 0x2

Speed: Up to 10 Gb/s x2

Current Link Width: 0x1

Cable Firmware Version: 1.1.0

Link Controller Firmware Version: 0.14.0

5big Thunderbolt 2:

Vendor Name: LaCie

Device Name: 5big Thunderbolt 2

Vendor ID: 0x3

Device ID: 0xA

Device Revision: 0x3

UID: 0x0003000052300C10

Route String: 303

Firmware Version: 24.1

Port (Upstream):

Status: Device connected

Link Status: 0x2

Speed: Up to 10 Gb/s x2

Current Link Width: 0x1

Cable Firmware Version: 1.1.0

Link Controller Firmware Version: 0.14.0

Port:

Status: No device connected

Link Status: 0x7

Speed: Up to 10 Gb/s x2

Current Link Width: 0x1

Link Controller Firmware Version: 0.14.0

It’s video files - on 2 LaCie 5 Bigs (about 16 TB) daisy chained to the computer. They are not showing up in disk utility. I’m not the only person to have experienced this problem. Just wondering if anybody knows a workaround for it yet. I’m pretty sure it’s to

do with High Sierra’s settings for the thunderbolt ports. Before High Sierra everything was fine.

You're not thinking about what I'm saying, or else not reading it properly.

Like I said before I've done all that basic stuff on the phone with Apple Support.

I'm up to trying this solution - https://youtu.be/ikBTrqoqjDg

and they agree it's a good possibility for getting it working again. Wondering if there's any easier or better way.

Yes it’s been very painful : ( Only good thing is the Mac help person really went out of their way to assist. She said she’ll keep looking for a solution and if she finds one will get back to me. I’ll let you know if she comes up with anything else. Thanks for responding to me on this 👍

After days on the phone with a helpful Apple tech support person, it turns out that this problem is caused by the High Sierra firmware update to the Thunderbolt port, v22.1, which cannot be rolled back to an earlier (working) version. It causes devices attached to the ports to randomly disappear then reappear later after restarting or resetting. In my case it took repeated restarts over 3 days before my LaCie drives showed up again. There are numerous reports of this problem online dating back 2 years. It’s a disgrace that Apple have not yet resolved this issue.