Yep, had a relatively cheap scope just decide to not hold zero once. Was out shooting the day prior and it was spot on. Had a huge 8 point whitetail @ 75 yards with a solid rest, remember thinking this is a chip shot. At the shot he just stood there and I was shocked, thinking why isn't he crappie flopping on the ground? Took me a second to come to my senses and run the bolt, that's when the doe he was bulldogging took off with him in tow. They ran across the 350 yard field and when I went to check for blood they ran back across at the far end, unharmed. I took my water bottle and placed it at 100 yards on the side of a hill and was shooting a few feet over it.
Have also had a mount come loose and cost me an elk, that was an expensive one.