The only thing I can think up is the blood shrimp.
The clowns used a hiding spot that the shrimps too over. And it's where I found the one this morning dead. Idk
Seems unlikely, more likely the shrimp pulled the clown over after death. Any chance of fighting? How old/what size were they, could they have been trying to establish dominance? Perhaps the pink spot? For some reason I feel like aggression was involved based on the fact that clowns tend to be hardy and that your other fish are alive.