G-Speed Shuttle XL not mounting on 2 macs

I have a G-Speed Shuttle XL connect to 2 iMacs via Thunderbolt 3.

The unit will only mount on 1 mac at a time. Whichever Mac is switched on first is the one it mounts to.

Obviously this is hugely frustrating as I need it to mount on both machines.

Can anyone help?

Thanks.

You cannot mount one drive to multiple computers at a time. This is the case for any drive. These are Direct Attached Storage devices and it will only work on one computer at a time.

The reason for 2 ports is for Daisy Chaining, not attaching to multiple computers.