I sometimes get wrong laser lines and arty position.
That's because server sends approximate data about everything thats more than 50 meters from you. Just in case you use some shady mods to have advantage. 
Cant be fixed, unfortunately.
Well, that makes sense

some more about both aim mods;
I'm using a sniper mod which can zoom upto 64x in sniper mode, and I need to zoom out (back to 4x or 8x) to lock on a target, otherwise it does not do anything.
Using the alternative arty view when using an arty (pressing g by default) cannot lock again.
Achilles aim mode sometimes aims to the bottom of the tracks, almost the ground, it cant evet hit the tank. And sometimes just the opposite, above the tank, to the air.
I think you are aware of these issues, im telling just in case you are not :p
Edit: Well now it can lock on target when zoomed in up to 32x, I dont know why I had problems before