AA bug or help needed?

[PlasmaKrab]

Gun has vision 0, but i think the gun is radar controlled due its high cost (fire control 105). Vision in scenario is 15.

That's it, Fire Control above 99 is AA radar, so according to what Andy just said it will be able to see through smoke and some amount of trees at a distance.
And indeed your AA gun mut be on a hilltop somewhere if it is able to catch you landed.
I hope you invested in some SEAD planes!
Else, if that guns has been shelling you for some time already, you should be able to see at least the gun itself or a cloud of smoke where it is firing from. Then just beat it senselessly with all the arty you have (I hope you have at least some) and try to move your helicopters away while the gun is retreating.

If you have neither SEAD aircrafts nor artillery, well...