New LaCie d2 Thunderbolt 3 drive & incessant "Disk Was Not Ejected Properly"

My new LaCie d2 Thunderbolt 3 drive is connected to a 2018 MacBook Pro 15" with Touch Bar & Touch ID via an OWC Thunderbolt 3 Dock. All connections are Thunderbolt 3 using Thunderbolt 3 cables. I bought the drive on October 20, 2018, and formatted it and created the first clone of the laptop's boot disk with SuperDuper! soon thereafter. Until last night I had no problems with it. What changed last night? After running the first scheduled backup of the boot disk with SuperDuper! I noticed some hours later that the disk had disappeared from the Desktop. Although I was able to mount it again using Disk Utility, I checked all connections and discovered that I had mistakenly connected the disk via its USB-C/USB 3.1 to the dock's Thunderbolt 3 port using a Thunderbolt 3 cable. This is a valid connection, but presumably isn't the reason for paying a premium price for Thunderbolt 3. So I reconnected the cable to one of the drive's two Thunderbolt 3 ports. Since the "Disk Was Not Ejected Properly" has been a regular feature of Notifications. Sometimes the disk actually no longer appears on the Desktop. Other times it is there despite the message.

I have read and can certainly believe that this is caused by the drive trying to sleep when idle, and this is the tenor of similar posts on this forum. Unfortunately, in contrast to other LaCie drives that I own, this one does not have the On/Auto/Off power switch that would allow me to override sleeping. This is supposedly possible using LaCie's Desktop Manager, but it doesn't seem to work, finding neither the d2 Thunderbolt 3 disk nor the LaCie Porsche Design USB 3.0 | USB 2.0 disk connected to the same laptop. As the Porsche Design also lacks a power switch and presumably sleeps, too, it would seem that the problem is with, or at least aggravated by, the Thunderbolt 3 connection. Perhaps the OWC dock is not entirely faultless, but I have just succeeded in connecting the Thunderbolt 3 drive directly to the laptop and have not -- yet? -- received the ominous message.

Has anybody experienced the same problem? Any suggestions, particularly about keeping the external drives from sleeping? The System Preferences > Energy Saver is already configured not to put external drives to sleep.

Thanks