I’ve had that too Andree – invisible sims who reappeared (hoorah!) but then turned invisible again (booo!). Last time I tried to play my main game there was a neighbour who had turned invisible indefinitely - I only spotted him because his thought bubbles were floating above the lawn outside his house. However the freezing-up in that game is so bad now that I cannot play it any more, so I can’t investigate further with those sims.
I did test an invisible sim that I could still control – I could open the fridge (just see the door opening and closing) and I could send him to sleep in his bed, which would create a bump in his blankets to show that his body was lying in bed but he himself was still invisible. Looked really weird. Also if I right-clicked him to lock the camera onto the invisible sim and then walk about, the camera would go up and down stairs and around and about with the sim.
