Kindle app for iPad install problem

[iMore Question]

I have downloaded the kindle app for iPad, from the apple site( IPad Air) this was not easy, as it took several attempts. Having done so, I downloaded a book successfully, but two days later the app disappeared and the app icon is now always " blacked out" on the home screen and underneath it says "installing"vand just does not install, but don't know why it needs to re install?