Scanbot is my go-to application for quick and easy document scanning on iOS.
If you are experiencing frequent crashes with the application be sure that you scan under 40 images at a time. I scanned 70 images and the app crashed on me, so i had to re-scan my pages.
I reached out to Scanbot about this issue when this happened, below is their reply.
Really sorry to hear that. There was a bug with pdf handling and this might have been a remnant of it. While we are working on smoothing things out completely, you're safer off scanning in batches of 30 or 40 pages of a time.
Hope this helps.