Achievements on MCPE aren't working. I complete them but they dont show up and I can't get rewards or any G.

Since about a week ago, I haven't been able to unlock any achievements. For example, in one of my survival worlds I unlocked the achievement "It's a sign!". That was the last achievement I unlocked. Then, soon after that I went on the same survival and found diamonds with my iron tools and built a nether portal. Non of the achievements were unlocked, as well as the rewards. Now any world that has achievements on won't unlock any achievements. I think Minecraft isn't reading that I completed them. And every achievement has a picture that goes with it, like steve in diamond armor for the adventure time achievement. Now the image for all the achievements is a blank person with a question mark. Please fix this bug, I'm a huge fan of the game. Thank you.
My gamertag is RadMedusa13.