I was having a lot of issues with the mobile artillery saying they would fire and then not doing so.
I was testing this further and decided to play as the arty myself, instead of using the support modules.
Upon doing so I realized in the arty computer the red line that represents the minimum range does not represent the actual minimum range as I am not given the option to fire until a good 1/3 into the "good to fire" zone for any given range load.
It seems the AI also uses this as a check as it will say negative (when using the module) if it is inside or outside the good to fire zone but will claim it fired when it did not if I tell it to shoot in that area that it claims is good but is not. I know I worded that weirdly, sorry.
And no, its not ammo. I have plenty.