Hello there,

If the client files are damaged, or the optimisation process is skipped or restarted, you will incur a download. This is because the download cannot recognise unoptimised files, so will need to download them again.

If you are having to download more information at this time, please just let it complete, as once done it shouldn't ask to do this again, and the reoptimisation process should save hard drive space as well as allow for smoother future patching.