50 Elite Co-op Kills

Another possible bug for 50 elite co-op kills. So, I started with one character could not get past 20 co-op kills. I deleted him. That is when I found out you have to do the event to get all the achievements. Well started a new charc ran her through the event at least 10+ times and still have no achievement. So my conclusion is that deleting a charc while trying to get achievement locks up the achievement. Will post more information if I find out that this is incorrect.