Invisible dragon

During our game, we had gotten the first drag. After a while drag had spawned again and we all went to go and grab it. But as we entered the pit (and prepared for a teamfight) Drag was missing. We had asked the other team whether or not they saw Drag and they also seemed to not be able to grab it, so we all assumed that Drag was gone forever and didn't bother anymore.

After a while, our Ezreal decided to attack-step the pit and it seemed that Drag was there the whole time, but untargetable and invisible. We managed to grab dragon despite having no vision of it at all. Afterwards the Drags after next were normal and completely visible. I have no knowledge of how to reproduce the bug, but this was the best description possible.