For me on PlayStation 4 it happens to my young adult and adult sims. I only play on normal speed.
It always seems to happen with the "enjoy company" "see what's happening" "listen to 'sims name' question" it's the little white icon with the two people next to each other that's autonomously queued during certain interactions that remains at the bottom of their queue while other conversation icons are happening but it just gets stuck there crossed out if you cancel it.
I've also had it happen when my sim autonomously wants to talk to an NPC that is in the process of leaving or has just left the current lot or venue, or if a family member is going to school or sleep and they wanted to talk to them just before they left their home lot or got into bed.
I've also experienced it with occult sims, mainly a spellcaster that transportalates to join a conversation that has just ended and a sim that wants to talk to a mermaid just before they jump into the water and change into their merform, as soon as their icon changes into their merform the icon gets stuck in the non mermaid sims queue and can't be cancelled.
These are all the scenarios I've had it happen and travelling to another lot usually gets rid of it for me.