Friendships/Relationships Diminishing For No Reason?

I've noticed this a lot too, I never looked into as I thought it was just a visual bug, I only notice mine when I switch characters in a household or if a sim gets in/out of bed. But did wonder why there was negative friendship points appearing randomly, glad I'm not the only one experimenting this.
I will update this post if I find any new information that hasn't already been mentioned above.