Q: Encrypted SSD Start Up Failure

Hi

I bought an external SSD to address the slow internal 5400 disk in my 2014 1.4 GHz Mac Mini. I attached it to the mac mini via USB 3.0, installed El Capitan and faced no issues (felt like a new machine with a 4x faster disk). The problem is when I try to attempt to encrypt the drive using FileVault. After selecting reboot, the machine will not start up. All I get is a blank screen, nothing else.

Here's the confusing part. I then attached the same disk (via USB 3.0) to a work macbook pro and booted off it successfully when in the same encrypted state. The macbook seems to have no issues with the encrypted drive so why does the mac mini.

In order to get it back working on the mac mini, I have to use the macbook to decrypt and it works fine after that on the mac mini. How can I boot off an encrypted SSD attached to my mac mini?

Thanks