I just completed the daunting task of beating the campaign legendary solo. However upon completion i recieved no achievments. Neither for the solo beat nor the legendary complete. My service record shows 15/15 complete legendary missions, but only 93% complete towards achievments. HELP!!!
If you haven’t already overwritten the checkpoint, I found a solution for the Normal difficulty achievement that should work for you as well. If all the levels registered as completed (including getting each individual achievement), but you didn’t get the campaign one, I found I still had a checkpoint directly at the end of the final mission. Just to try, I walked up that ramp again, finished the level, went through the cutscenes (watching them, just in case) and boom, Normal campaign achievement. This might work for yours as well.