The stock version (found in data/itemCoillections:
itemCollection_Ammo_all,,,
Ammo_AmmunitionBox_Generic_AC2,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_AC5,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_AC10,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_AC20,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_SRM,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_LRM,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_MG,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_MG_Half,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_LB2X,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_LB5X,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_LB10X,AmmunitionBox,0,10
Ammo_AmmunitionBox_Generic_LB20X,AmmunitionBox,0,10
I don't know if the JK thing has some other way of getting you the ammo, but a simple fix would be to add those lines back in.
Or just replace this line in JK_VariantsCampaign's mod.json:
{ "Type": "ItemCollectionDef", "Path": "itemCollections", "AddToDB": false },
with:
/*{ "Type": "ItemCollectionDef", "Path": "itemCollections", "AddToDB": false },*/
The itemCollection from the mod doesn't serve a purpose anymore, anyway, since 1.9 added the half ton MG AmmoBox to the game, which is why the mod changed the file.