I found diamonds two separate times and both times I got no achievement for it. Though I have received some other achievements in that world often very delayed. So it seems like this one is being stubborn as I haven't received it and I think it's been about a day of playing in that world.

Also the achievements get in the way when playing as they pop up and take over a third of the screen length (idk how to change that if that's possible). They fire off delayed as well. <-These two issues are probably different tickets.