I faced one strange issue very recently in my FDE machine.
I am using FDE without media encryption, due to some reason I connected my external hard drive to backup my files from my machine.
Soon after I connected it was not detect so I un-plug it and checked if it detects into some other machine. It was detected as expect but unexpected it was started getting encrypted.
Was it happened due to "Allow encryption of volumes that were detected after the initial installation" (or) due to some other reason.
Why I am asking this here as be cause I enabled this in my Endpoint server FDE policy..