I see the same behavior on several maps so I don't think it's map related. The gunner is getting sometimes between 4 and 6 laser range returns. If you select which return looks the most accurate with the 1, 2 or 3 key (1st, 2nd, Last) and then press 5 to FEED the information into the fire control he will usually fire however it's not always dependable. I thought perhaps this wasn't a bug but how the laser range finder works in real life and something the real crews had to contend with.
I make sure to press 4 to Battles Sight and then Numpad 0 to reset the range finder and sometimes this does help because if the gunner manages to get 1 return he will go to town and engage multiple targets accurately even without the commander re-setting between each engagement but sometimes he gets stuck with the multiple returns and the reticle moves around a bit on the target and you get the "we got problems" audio. It also seems to make a difference what kind of round is loaded as to whether the gunner will fire, if there are obstructions or the target is over 2000 meters the gunner is reluctant to fire anything other than SABOT rounds.
One last observation is that when the gunner gets multiple returns if I then take over from the TC position I can usually lase for one return, so in that case I'm not sure what the difference is between the AI and player.
I have no experience whatsoever with any LRF equipment so what is a bug and what is intended as simulation for the M60A3's quirks is something I am very curious about. Appreciate the team looking at this behavior.