Files vanished during transfer

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I am setting up a new computer and was transferring a large folder which basically contained my entire organization. The transfer started and then "aborted". When I went to try again the folder was empty save for a few files, a fraction of what was in there. I have looked in OneDrive where I back things up, that too is empty. On the old computer...gone! The new computer, the same.

This is really a nightmare. Any help would be so, so, so appreciated.