It happens from time to time. Sometimes, they can still be looted, but not from where the corpse appears. Walk around some to see if you can find the prompt to loot.
That boss does it all the time. If it dies during its jump, it gets desynched so the body looks like it's in one place but the server sees it in another pretty far away.
Best option is to just run out of the area a ways and then run back. You need to get far enough to reset the area, and then when you come back the body will be in the right place to loot