External Hard Drive unrecognized

The cable, cases interface or drive itself may be faulty.
Test these and replace as needed.

UBCD has drive makers diagnostic tests or download the free test from drive maker site. http://www.ultimatebootcd.com/download.html

The usb drive is a box commercial one (Seagate Back Up Plus) and I used the cable provided in the box. The cable would be the only easy thing to replace. However, it looks to me that the issue is more windows related than hardware. Indeed, most of the time this external drive just works well

check in the energy settings that the drive is not turned off by windows to save power

The usb external drive is not powered by the USB but has its own separate power supply. Should I still modify the Windows power settings? If yes, which ones

My question is : why does the value revert back to 1 by itself? Why is this linked to my issue?
And is there a way I could avoid this, or have a program that I can double click to reset the value to 0 without opening regedit

This is caused by some program which you are using. Try to check when exactly does this start happening. The must be some logic.

tx for posting details Michael, but i thought the energy settings (from control panel) were known
weakcontacts would not reset registry settings imo

Thanks all
I did change the power setting just in case
My USB external is HDD not SSD. It is a commercial 8TB "Backup Plus Desktop Drive" from Seagate and has no manual switch.
When Windows no longer sees it, I still see the LED lit on it so it is still powered. When that happens, I look at the device manager in the configuration panel and I can see that the USB 3.0 bus controller has an issue (exclamation point). So I decide to reinstall the driver (Texas Instrument) but Windows refuses to run  the driver installation program unless I change the value "EnableLUA" from "1" to "0" in Regedit. I modify this value, reboots and the problem vanishes without even the need to reinstall the driver. But the problem comes back after a few days or weeks.
I have been unable to find a diagnostic tool on Seagate website. All I can find is a utility to backup data, modify performances but it does not seem to include a diagnostic tool.

What is the exact model of your drive? Note, the Seatools work with internally connect drives. Means you would have to open the box and get the drive out.

As mentioned above, it is a  8TB "Backup Plus Desktop Drive" USB 3.0 from Seagate

8TB? Then it is a RAID device and you cannot check it with a drive test utility. So have you checked when exactly the problem occurs? Are you running any kind of backup software at the moment or before the drive gets unmounted?

No way to get higher than 2.2TB on one volume on MBR, regardless of the OS, BIOS
Must use GPT to have one volume as 8TB

I have not yet linked the issue to any running program. The drive capacity is indeed 8TB and came formatted for windows when I bought it