Sim who asks for mark of Edith functionally becomes Edith

I have a related issue which brought me here.

Edith is randomly turning into Nathanial McCoy, he also does the squatting thing.

My interaction options with him are the same as for Edith, however the game recognizes his name as Nathanial and he is different to Edith in the friend panel.  I can ask him for the "Mark of Edith".

When I am not talking to him he does normal sim things, he's at my house drinking water and playing with clay, but when my sim is interacting with him, he does Edith animations. It's actually quite creepy and I initially thought maybe possession was a storyline/lore thing.

I have high friendship with him but none with Edith in the friend list. 

As this is a new pack for me I can't tell when this first appeared.

I have most packs. Not Enchanted or Batuu and missing some stuff packs and kits.

I do have MCCC installed.