Randomly regenerating NPC's

I have been campaigning with an NPC called Raphina Nierbloom. As I am progressing the story, about to have an encounter with a creature, I notice the “Characters” section doesn’t say “Raphina Nierbloom” but just “Raphina”, and a new, randomly generated NPC is there. Yet the story is using the correct Raphina Nierbloom.

However, when the encounter starts, it’s suddenly this new Raphina that is in combat, not the correct one.

This has happened several times, unfortunately :(