How to fix external disks that keep disconnecting when in fact they are still connected

No one here is privy to Apple's development cycle, or their knowledge of the bugs.

http://bugreporter.apple.com/ you can connect to after a free sign up with http://developer.apple.com/ and you can get a non-disclosure agreement feedback from Apple about reported bugs, which may not be annunciated on this board here.

That said, there are other known bugs with disconnecting hard drives ->

• Insufficient power. Energy Saver and Power System Preferences/Settings from the Apple menu offers a put hard drives to sleep option, which can solve many of these problems
• Some third party drives will not respond to the turning off of put hard drives to sleep, and will still sleep regardiess, your choices there are:

1. Use an AC/DC adapter based hard drive.

2.Use an AC/DC adapter based hub

3. If the Mac has a USB-C power supply, use a pass through USB-C hub that adds power to the hub from the Mac's USB-C cable.

4.Be sure your USB-C cable has a lightning bolt icon on it. This indicates thunderbolt compatibility and more video and data support than the straight charging cable that ships with USB-C Macs.

5.Use Screen Saver instead of Energy Saver. For laptops, this means not closing the screen lid, and dismounting the hard drive before traveling in sleep mode, or even better off, just shutting the Mac down. That's a better choice since it won't accidently wake up and overheat.

A simple desk lamp that plugs in with a two three prong standard connector into the wall operates off Alternating Current (AC). Most portable devices work best with Direct Current (DC). Any device that uses a brick to a cord on the wall converts the AC power that your power company uses into the DC power the device uses.

That explains also why the AC/DC bricks themselves run hot. They are changing method of electricty with resistence and a mini-transformer. The Mini is somewhat between a desktop and laptop Mac but doesn't have the large power supply an iMac or Mac Pro desktop has, so it can't supply the power needed for many external hard drives. That's why I recommend a completely external power source.

Is your hub a USB-2 or USB-3 hub? Or is it a USB-C hub?

So a hard drive or hub that uses an AC/DC brick like you might find on a portable wireless phone, an old walkman, or CD player gets its power directly from the house power, and completely doesn't care how much power it is getting from the computer, and can focus on data transfer. Many hard drives get their power directly from the Mac, and that's usually not sufficient, unless the Mac is itself a desktop Mac like an iMac or a Mac Pro desktop. And even the iMac sometimes doesn't have enough power. These SSDs really need an external source of power either from the hub, or their case's built-in power supply.

The SSDs you find in portable external SSD cases usually are just portable SATA drives, with a USB-SATA data port adapter to connect to the external USB cable.

TripLite makes external USB-SATA adapters you can plug the SSD into with their own AC/DC power brick. And there are manufacturers that make power supplies inside USB cases to attach SATA. Those are far better than the mini-portable SSDs in terms of supplying sufficient power for the drives. Western Digital actually makes a few of them.

https://www.amazon.com/RSHTECH-Enclosure-External-Docking-Station/dp/B076HNWDMX

Just a quick search on Amazon I found such an external docking station which can be used with SATA hard drives, which you can see that AC/DC brick on the side. It is these kinds of things that will enable your SSD to work smoothly with any portable or small Mac. Without that separate brick, dropped connections can be frequent. A hub would have a similar power supply like that if it is truly a powered hub. If it isn't there, it is gettting its power over USB from the Mac. In which case, it isn't giving enough power to the hard drive.