The issue is that I was wearing my Elytra, it wasn't near breaking or anything it was like just barely under halfway with it's damage. I had put mending on it so I could recover it with EXP and as soon as I just began doing that, I realized it wasn't on me anymore. It just randomly disappeared?? I don't know why, I was wearing it one moment and literally just a moment later it was gone. It didn't break, I wasn't using it. It just disappeared?? I really don't know why or how to recover this, it's a huge game breaking issue imo that really needs to be fixed, this was my first time ever getting this item so it really sucks losing it for no fault of my own.

Edited to Add :: I was playing in survival. I haven't used any cheats or anything because I wanted the achievements, if that helps at all.