Sim vanished - is this a bug?

I moved Lou Howell, who was living with my sim, into a different household and moved my current sim to a different world. 

Lou has now disappeared from the whole game, as if he never existed. Nothing in the friendship tab, nothing in the worlds, the memories have replaced his name with ___ and he is no longer in the family tree - it’s like he hasn’t existed.

This is a first for me, I’m using some mods but I was playing them with no issues, all are up to date. I’m playing on PC and just bought the growing together pack. Is this a known glitch or something new? 

thanks