i think its a bug it happens wen a alien chamber is there before u build turrets right close up to it but the turrets dont fire even if its right in its face

I do believe that the real problem here is that a turret will sometimes not fire against a structure that is higher or lower (y-axis) than the turret. I tested this on ns_veil in cargo. A DC that was built on the stairs was not fired upon by turrets that were higher than it in the hallway, but if a skulk was at the same position (or lower), it would be shot by the turrets.

I think sieges won't sight anything in a case like that either, but they will shoot it if you spot for them. So, it's probably an LOS problem.