In A1 the classes SoldierWB/EB/GB/Civilian are actual units with scope 2.
Since A2 they are just base classes with scope 0.
To achieve A1 missions compatibility, the said classes need scope 1 at least.
However when doing this, all subclasses will now use the model defined in those classes and no longer the model defined in the subclasses. {F19942} {F19943} {F19944} {F19945}
I assume the problem comes from infantry subclasses in between have scope 0 and somehow confuse the engine.
Sample
SoldierWB: CAManBase
scope = 1;
model = "\ca\characters2\USMC\usmc_soldier";
class US_Soldier_Base_EP1: SoldierWB
scope = 0;
class US_Soldier_EP1: US_Soldier_Base_EP1
scope = 2;
model = "\ca\characters_e\US\US_rifleman";
Added another demo mission on Desert world (OA) that has all A2 and OA models present.
The text file contain the scope values for A2 and CO infantry classes as reference.