USB-connected SSD disappeared from explorer  

George, I'm puzzled by the USB sticks working and external USB drives not working. I'm sure you are providing power to the external drive if it needs that since you tested it with the other PC.

I have not used any registry repair or cleaning software in years and don't have any recommendations at the moment.

https://blog.malwarebytes.com/threats/registry-cleaner/ see this.

I believe if Malwarebytes finds malware in the registry, it will attempt to remove it or first let you know and decide if you want it fixed.

@Tekkie Boy,
Are you able to fly out from Germany to Norway to help my friend George here

Yea, I am really puzzled too. The USB drive get the power from the PC's USB port. When I connect the drive the blue light indicates that it is powered and when I hold it to my ear i can hear and feel the fan running.

It has a fan and power via USB - not external power supply like mine?

Would you recommend to run Wise Registry Cleaner again and let it fix the listed errors?

togel said:

Would you recommend to run Wise Registry Cleaner again and let it fix the listed errors?

I don't use such products, so I would defer you to Google and see what people say. @Tekkie Boy may have some suggestions on this when he gets here.

Which Registry Cleaner to Use? please see this

Yes, it is a Seagate Expansion Portable Drive, 3TB. The other portable drives is 1 Verbatim 1 TB and the other an old Lacie 500 MB. But they all connect to the USB port...