One thing I can think of is if the block size for the device got changed to a larger number than the drive can handle. If the block size was increased, the backup would complete successfully, but the data would not be able to fit into the restore buffers. The errors that occur when the block size is too large varies, so I don't know for sure if that's the problem.
Try lowering the block size, and try a new backup and restore.
If that doesn't work, check the properties of the drive for the number of Hard Read and Hard Write errors. If there is more than 0, then drive is suspect, and you should contact the manufacturer.