I have several bugs with the achievements and it's getting even worse. So lets start:
1. For a long time I had from the long time challenges a "1" displayed, like I could collect something but nothing was displayed
2. After sacrificing 50.000+ and skipping an achievement and getting two at once, I could collect something but then there was a "2" displayed. So obviously this happens if you do more than one challenge at once and the second (or third) achievement is unlocked but you can't collect the reward
3. Then I had some server issues... and after restarting the game it got really weird. My achievement challenges went down from 97 to 91 completed to something about 80 now. Why? But I could collect some more rewards... okay (don't know if they are new or if I had to collect them again, because I achieved that already some months ago)
4. Now I have number "6" displayed at the long time challenges and don't know how to collect the hidden rewards...
Anyone with the same problem and a solution?