I remember that happening a few times. One Sunday morning my son went up to a young elder and said "Hey, I thought you were giving the talk today in XXX XXXXX. The look of horror on the Elder's face! He had forgotten. He had to hurry home and get his notes and rush off to a hall in another town that was a bit of a drive.
On another occasion, an older brother showed up at our hall after we had given up and gone to the Watchtower Study. when he got up to give his talk afterward, he told how his car would not start that morning and he borrowed his neighbors. It was a big car that cruised pretty easy and he found himself being stopped by a cop. The cop asked him why he was in such a hurry and he told him that he was a minister and he had car trouble and was running late. The cop was sympathetic, but then as an after thought, he asked him what church. As soon as he said it was the JWs, the cop wrote him a ticket. He obviously disliked JWs. But of course it was put across as Satan's doing and the persercution thing and all. The guy was a horrible boring speaker. I think Satan was trying to do us a favor.