When you "save to camera roll" from Lightroom mobile from a raw file directly imported into Lightroom mobile (or even a smart preview file synced from a computer, Lightroom exports jpegs with the dimensions from the original file. For example if the original file was 4016x6016 pixels and I crop it heavily to only 1000 pixels across or so and then hit "save to camera roll" it comes out as a very blurry 5676x6016 image. It should of course come out at the maximum cropped dimensions instead. This issue was discovered in this thread on Adobe's U2U forums: Cropping RAW files