To get the immortal medal you have to survive all the rounds in a game of breakout (aka not die once). And in the extermination breakout mode, all you have to do is be alive when the round ends, right? I did this and didn't receive the immortal medal. I re-watched the game afterwards and made sure I was alive at the end of the round each time, and I was. Can anyone provide some clarification to why this happened?
Immortal Medal Confusion