usb – DVDs not mounting in Ubuntu 20.04 – works fine in Windows

I have an Hitachi LG-WH16NS6 SATA DVD and Bluray drive mounted in an OWC Mercury Pro external USB 3 caddy.

When I connect the device to my machine and try to insert a DVD under Ubuntu (20.04 LTS), the disc spins and the drive tries to read it but the disc is never mounted.

Eventually, the drive spins down. If I try to shut down or restart the computer after this, the shutdown process hangs and I have to do a hard reset.

If I start the computer and boot to Ubuntu with a disc in the drive, for some reason the partitions efi and boot are present in the file browser (which they are not normally). The disc still doesn’t mount.

Paradoxically, I can read and mount Bluray discs with the drive in Ubuntu without an issue. Also, my machine is a Windows/Ubuntu dual-boot setup and the drive will mount and read DVDs and all other discs in Windows 10 without any issues. All the discs that don’t mount under Ubuntu mount and read without issue under Windows, so I don’t think that I have a bad drive or bad media. I have tried connecting to a different USB port and I have tried a different USB cable, all without success.

I have installed the udftools, libdvdcss, libdvdread4 and libdvdnav4 packages under Ubuntu but this has made no difference to the behaviour of the drive under Linux.

How should I go about debugging and fixing this issue?