It might be that when you lase there is very close terrain in front of you, or some power lines or something else that is giving you a bad reading. Having to lase 3 or 4 times might be a symptom of that, especially since you can get it to work at other times.
It might be worth you flying to the same spot, sticking into an autohover and then taking a really good look at your surroundings, then maybe moving about a bit to see if the problem persists. I get it sometimes when I'm just above a ridgeline that I can use for cover, and I'm not quite high enough. A couple of extra metres normally does it.
I'm not saying this is definitely the problem, but it's possible.