Umbral Gems

Hey guys, I’m pretty sure this might be a bug too as well as spoilers.

I am 97% convinced the 4th umbral gem despawned during my fight with the Orthon. I’ve gone to my save right before the fight and it’s still there and the save right after the fight and it’s gone.

I’m like 4/5 hours past that point now and it would really kill to have to go all the way back. Any way to solve it without all gems?