Ah, I understand.
How do you move sims out? Do you move them directly into the other house, or do you make them 'homeless' in Household Split? A homeless household can't be the active household, so maybe you could try that, and then move them into a house later? Does that make sense?
If the problem is switching active household, maybe this will make the game realise which house is the active one.
I really don't know, as I've never had this problem. I'm just spitballing ideas here.
Sent from my SM-G935F using Tapatalk
EDIT: I just reread the threat and saw that that's exactly what you've been doing, so ignore this.