Sims forget already existing relationships

I have been noticing this happen more and more recently, including forgetting their own family members with whom they had good relationships. I am not sure if this is the reason but it does seem to be occur more frequently when swapping between different households? I had sims completely forget their roommates when i left to play in a different household. All of my sims knew one sim who had died and suddenly none of them, including her siblings and uncle, had ever met her before but she's still on their family tree.