Mercury Elite Pro external hard drive won't mount on M1 Macs but mounts on Intel Macs

Initial setup: iMac (Late 2014) running Big Sur—this is my primary Mac. I also have a MacBook Air (M1, 2020) running Monterey. I use this infrequently and when away from home, so it has only the files and applications I may need when when I'm on the road.

I have a 2TB OWC Mercury Elite Pro (USB 3 with USB+1 Port) that I purchased in September 2018. I had been using it as a destination drive for my Carbon Copy Cloner backups of my iMac. It worked perfectly up until my iMac went out of commission recently. I'm planning to switch to a Mac mini when the next models are released, so I figured I could get by with my MacBook Air in the meantime.

I needed to pull some files off of the Mercury and onto my MacBook Air, but no matter what I tried, the Mercury wouldn't mount on it. I do have a number of other older drives (two ioSafe G3s, a Western Digital Big Book, and an ancient 320 GB imation drive) which all mount fine on the MacBook Air. Here is what I tried with the Mercury.

• Checked Disk Utility--never appears in sidebar
• Attached Mercury with a USB-A to USB-C adapter (third party), Apple's USB-C Digital AV Multiport Adapter, an Anker USB-C hub, and a powered USB hub plugged into the Anker dock
• Swapped USB cables with one of the ioSafe drives
• Checked About this Mac > System Report and verified that the Mercury does show up on the USB bus with each of the connections listed in the second bullet above
• Plugged a peripheral into the USB+1 port on the Mercury—that's recognized on the USB bus.
• Extensive troubleshooting with both Apple (phone and Genius Bar) and OWC

I did get my hands on an even older iMac (Late 2013), and the Mercury mounts fine on it.

Thinking it may have something to do with the operating system and not just the CPU, the Mercury has been tested with the following configurations (including the machines listed above).

My Machines

• Intel iMac (Catalina)
• Intel iMac (Big Sur)
• M1 MacBook Air - Big Sur (fresh installation just to test the drive) and Monterey

Apple Store Genius Bar

• Intel MacBook likely running Monterey
• M1 MacBook likely running Monterey

Each time the Mercury was plugged into an M1 machine, it appeared on the USB bus but not Disk Utility. Note that the light on the drive also didn't flash to show that it was being accessed. On the other hand, each time the Mercury was plugged into an Intel machine, it mounted fine. (The light would flash before it mounted to let you know it was communicating with the Mac.)

The working theory from OWC Support is that there could be a problem with the drive enclosure. Unfortunately the drive is out of warranty.

Has anyone come across anything like this and can shed some light?

Thanks in advance,

Paul