I presume the Agent is Pre-installed on the Image.
My guess is your imaging process is capturing encrpytion details from the prior image.

While I've never seen this before so this is a random thought...
Starting from a Clean OS Install that never had the ZCM Agent installed.....
Install the agent with the "-b fde" switch so the device does not install FDE by default and make sure the device initially registers to a folder that does not have FDE set to install.

Then when you image a device, it will be sure to not have any left over FDE stuff.
Then when you image, the device will install the FDE spoke after it is imaged.

But almost certainly it is about something with your image.

No other customer has reported this issue......

Service Request would help far more than sales.........