Do you have to save them directly on your computer?
Consider a second, dedicated HDD or, better yet, a SSD in your computer.
Can you attach a flash drive or SSD via USB port on your computer? Maybe just a simple flash/thumb drive.
Or map to another shared computer drive/folder if you have a home network. Make sure enough space is available.
Try downloading a couple of the onecloud files to test the process and verify good copying. Then download the rest of the files.
Just keep verifying that the copying is going well - no corruption and be aware that you may hit or exceed some "download" limit which may incur additional charges via your ISP.