I had uploaded an 82GB sparsebundle to Backblaze B2 over 3 days. Once done, I then proceeded to download it to verify it had completed successfully. From memory I quit the app in-between, but I could be wrong.
I left that running for the day or so, for it to get 64.29GB through the download, before my operating system complained it ran out of memory, as well as disk space (despite having 130GB or so available at the time of the download). I opened activity monitor at it turns out that Cybderduck was taking up 77GB of memory, so that is a large swap file it would have had (I only have 16GB of memory).
Screenshot of the situation attached, as well as of the disk space error.
I ended up quitting cybderduck and restarting the computer. I tried to resume the transfer, however I then got a permissions error, screenshot attached.