it is possible to destroy some of the cargo when you shoot any wreck for its loot.
it all depends on the firepower you are using and how many times you hit the wreck.
this may give you a diffetent result each time the wreck is looted.
but only quantity will change, not type.
unless reprogrammed wrecks appear to hold the same type of cargo upon reloot if of the relooting type or reset type upon each server reset.
and as wombat1940 you are using an autosave game you are in fact repeating the rxact same looting every time you do it, so it appears your rate of fire could be why the loot quantity is different.
if on the other hand your loot is changing from one type to another then you do have a rare occurence and it is either a miracle or you have stubled into the............"Twylight Zone" ............ !? ::::::::::: Try using low power wepons or shoot the wreck only with one gun one shot at a time, stop shooting immediately when thing pop, sometimes one shot is enough -