In my game I've mostly seen this occur when a Sim autonomously decides they want to play video games on a computer sometimes trolling the forums too. The main problem is they will drop their entire queue to go do this activity that you can't cancel because their is no icon and even pressing the cancel action button (triangle on PS) does nothing.
Back when Dream Home Decorator came out I used to see my Sims drop everything to do an invisible/uncancelable action which was eventually updated to be "Judge Decor"
