Bug in Steam/EA App achievements

I set out to platinum the game without realizing it had these kinds of bugs with the achievements. I got to the point where I unlocked all the achievements except for "I Am a Living Legend," which requires defeating all legendary enemies. It's strange that I didn't get it since I already have the tactical guide 100% complete, and to get that achievement I had to have defeated all the enemies.

This is my error report:  a19d99e6-08a9-428b-9dcd-d5953f61f91a