The paper ticket validators are as slow as the gate opening mechanisms, and at my station there's one gate where I rarely manage to get my ticket through. It's NOT my ticket being worn as it works everything else; just one gate.
There are also a few gates at the new northern ticket hall of King's Cross that can't read my Oyster either (again, same gates every time). Clearly the maker of these gates must be part owned by Bombardier or something.