Mount external HDD readOnly option

So the problem was with the cable. Apparently one of the small pins on the cable that connected the optical drive to the motherboard, got broken.

If it was a total failure of the drive this may have been more obvious, alas, it was not. It merely caused the drive to work in an unstable manner.

As soon as I replaced the flex-cable with a salvaged one, the problem disappeared.

Not sure if this will be helpful, but I just wrote a script to unlock and mount a core storage Encrypted Disk like yours for myself. I had the same problem where I could get the disk unlocked, but not mounted. I finally realized that I needed a command to mount it after it was unlocked.

In terminal, you first have to unlock the Encrypted Disk and then you can mount it with a separate command. For you, that would look something like this:

diskutil cs unlockVolume E2DB4126-C04C-4AE1-B1AC-CDFF0218D537 -stdinpassphrase 

You will be prompted for the password to the Encrypted Disk. After this, your drive will be in an unlocked and unmounted state, so you still need to mount it with this command:

diskutil mount E2DB4126-C04C-4AE1-B1AC-CDFF0218D537

In case you were wondering, E2DB4126-C04C-4AE1-B1AC-CDFF0218D537 is the UUID of the disk you want to mount. I'm no scripting or CoreStorage pro, but your problem seemed similar to mine, so I hope this can help you. I got all this info from the diskutil man page if you run into any problems.