I just got 50/50 perfects for a third time, but still no achievement. I made sure I finished the levels in order as well. So the only thing left I can think of is getting a perfect on the last day on the first try.
100k 17/07/10 - 200k 02/09/11 - 300k 02/02/13 - 400k 20/11/13 - 500k 25/10/14- 600k 15/08/15
Overachiever: 58 points - 16 Staff Clubs - 8 Subscriber Clubs - C/F Clubs 15-7-3-0 - 332 XB1 club points
Winner of GSL XII and XIII, MVP of GSL XII