Just make sure that everything you are Z sorting is on the right layer you should be fine.
To make sure, test your layers by setting visable and invisable then you can find if there is any sprites on the wrong layer.
You can also add this to the start of layout.
On start of layout > Move Sprite(or falily) to layer.... to make sure all sprites you are sorting is on the correct layer.
Or you can add a condition to your Z sort.
"is on layer" that way you will make sure you only z sort thing on that particular layer.
Nice one ... That was exactly the problem. I haven't debugged which are the offending objects but I have verified it by doing a mass move every tick , of all objects that are supposed to be on the z sorting layer , to the z sorting layer.
thing is , im working in C2 and this dosent give any problems in C2
it kinda makes me want to make the transfer to C3 but I was going to wait until we got the all clear from Ashley