Is there a cheat/hack that protects you being marked as HVT by commander? Because sometimes I cant mark some guys as hvt as commander. Or is this a bug? Any admin please reply to this thread.

Never heard of it. There might also be some kind of kill or points earned per life requirement to be tagged as an hvt

You can only mark someone who has got more than 5 kills without dying as HVT. AND he has to be shown on the map long enough for you to right click and mark him as HVT. In other words, if he is shown on the map for only shooting few times or by a motion sensor or T-UG, you probably cannot mark him since he might has already disappeared on the map.

The point was I had the chance to mark him as HVT. But everytime i try tagging him  he just disappear even if i put scan on top of him. And when I do that its guarenteed that I can tag hvt 100% success rate 24/7. So something is not right.

Is is possible that he was running Phantom perk and he didn't sprint at all? Maybe that will make him keep disappearing even under the scan UAV.

I don't know if there was a hack that can stop you from being marked but from the situation you post I can't really tell if it's normal or not.

That’s not something we’ve heard of as part of a hack, sorry. Not sure what would cause the issue you’re having. Although, BF4 is riddled with bugs, so could be that.