I have a MacBook Pro (2015, 13") with 2 Mac Operating Systems installed on it, one of them is the latest macOS High Sierra, the other one is OS X Yosemite, where High Sierra is the default. Today I was going to boot from OS X Yosemite using the Boot Manager (alt key during boot), but I noticed that Yosemite was gone, and there was a Recovery HD out of nowhere. I chose it to understand what it was, but the computer booted into Yosemite. Is there any explanation for this? Why would it rename itself to Recovery HD? This is just so annoying.
Not sure if this helps, but OS X Yosemite has FileVault. FileVault was on when it was normal, too.