Same happened to me on the rancor fight. The only difference? I literally cannot load back into that save as the game freezes every time iimmediately as i load in. I've tried clearing shaders, caches, verifying files, repairing files, everything i could find online. Nothing works. I'm once again at the mercy of EA to fix this broken mess they call a launch ready game, or start a new game for the 3rd time already. It's a * disgrace really.
At least when i died in my second save to another beast, that wasnt a legnedary enemy the game just crashed but i could load back in. Hopefully im as "lucky" next time.