Grain Science 1.3 had a bug relating to the way iOS was handling some of the user presets from earlier versions of Grain Science. This 1 bug could lead to a failure of many other parts of Grain Science, resulting in a crash. Wooji Juice has been working hard on correcting this!
I know this, because I've been bugging them about it! One of my presets from the video review was effected. When I launched the new update it checked its library and reported the Missing Audio files. At this point Grain Science attempted to recover the files, but they were not in my device's cache and unrecoverable. In cases like this you get a cute little icon letting you know there is a missing file for the preset, a vast improvement over the crashing you'd have previously.
Wooji offers a detailed explanation of the problem and fix on their blog. If you purchased Grain Science at version 1.3 or higher (late March and on) then you don't need to worry about any other this, as it only effected people updating from earlier versions.