Okay i will make it clear. It is some kind of graphic problem.
Where there should be reavers there is no sprites. I kill them in every encounter i get.
If i get reaver and mutants i only see mutants and they fight each other. I spill their guts as the text says but no reaver sprites.
And to be exact whenever a mission has reavers they are invisible to me but not to my charactes ofcourse who simply kill them.