I believe Marc Leishman made an incorrect drop at the Zurich Open on the 16th hole after his partner hit it in the water. He made his drop with no rules official present and he dropped closer to the hole.
The relevant rules is 17.1d(3)
Here is a screenshot from the PGA shot tracker. It shows where his ball entered the water (slightly above the “1”) and his drop should be along the red line, between the 2 yellow circles. He instead dropped closer to the hole, at #2.
Here are several other overhead shots. There is no rules official present when he made his drop. He should be dropping along the red line, but he drops further up the slope. He even adjusts further up the slope after making his initial line. He marks his line at the blue circle, which is clearly closer to the hole. Yes, the ground camera can add some distortion, but the overhead confirms that he drops in the wrong spot.
This makes the shot significantly easier. He chips in for a birdie and they win in a playoff.