I've noticed that this is starting to happen more frequent. Last weekend while shooting at a wedding reception, I stopped and focused on two women that were posing for the picture. The eye af locked on one of their eyes, but the focus continued to hunt. The camera was quickly switching from in focus, then slightly out of focus. It would zip rapidly back and forth. The lighting wasn't the best, but wasn't having issues earlier in the same environment. This has happened with different lenses, so don't think it's a lens issue. I ended up taking several shots to be safe, and later found that the focus was off on one of them. This could be a low light issue, but would think there would be more people posting issues about this. Haven't found much online similar to my issue. Thanks for any help!