Party corpses will often not spawn properly after their deaths.
Such as if they die from starvation, there corpse will not spawn.
I'm guessing you are playing v2.3? There was a bug in spawning the dead bodies (as well as some other sprites) because I updated some of the systems. It should be fine now in v.2.4 as long as you first transition to another room (there is a version fail safe in map transition) If it still happens after that, let me know!