Vmdk's wiped after startup

This is more of a warning and I’m not sure if its configurable or not. But here is what happened to me. I had a machine created through nebula that had two disks with esxi backend. I added additional 3rd disk through esxi directly. Then powered off the machine and powered it back on. The 3rd is gone…completely wiped out from exsi. Lost few months of data, which is huge issue for me and that was on 6.0.2 version. Is this really the intended behavior?