When my first one disappeared, I assumed I lost it in my inventory. But I found one yesterday, secured it in my realm, and today it's gone. It WAS secured.
I know they don't do anything, but for the grind I put in to get it, I figured I'd at least use it as a realm decoration.
We'll check out the logs to see what happened to it. I'll get back to you as soon as we figured something out, sorry for the inconvenience!