Sims forget already existing relationships

Having this issue too. I'm a rotational player with many households. So I haven't played this one household in a few days, when I looked at the relationship panels almost every relationship bar is EMPTY, even with his own brother.  He's also befriended a lot of his co-workers + ppl outside work and those are apparently forgotten too, like completely gone from his contacts. 

Now before you say, get rid of mods repair game etc, I did. I don't think it affects this issue because the lost relationship + contacts can't be regained after it has already happened. Other households does not suffer this issue.

Some minimal troubleshooting I did are:

• Brother got married and moved out of this household into his partner's house.
• Is it possible that this Sim got affected by a memory wipe power of an alien? I've never played aliens before so I don't exactly know how their memory wipe power works.

It's not the end of the world as I can cheat all these relationships back but it'll be such a monumental work because this Sim has a lot of friends :|