Sometimes if a tank is behind a hill, he is close enough to the hill to get his gun veiw over it, he appears as part of the hill,Shoot the hill.
Warping or something like warping may be causeing what you see, if an object is fading in and out until it is no longer seen, film it, this is a bug.
Warping, I may be wrong here, or maybe I wanna think people are better then to cheat, but, I have seen enough people trying to stop warping in the TA to realize that warpers are prolly not doing it intentionally, they have a tech problem.
And if they are doing it intentionally, I really don't know how they could keep guns on the target, if they did it they would do it in defence trying to avoid getting hit,I would think.