The script to revive characters is triggered during XP distribution; if the character has been dead from the start, that script isn't being called. In your case, please try the following test: load your game and run this command in the console:
$gameActors.actor(ID).setHp($gameActors.actor(ID).mhp);
Replace "ID" with your summon's ID from the actors list. This script fully restores HP, so the character should come back to life and be ready to be summoned again; then, check if the behavior has been fixed.