I just had exactly the same problem as kavka described.
The whole file content was deleted and I “couldn’t copy” it from file file recovery window. At least that’s what I thought until I saw that this version was 0B size. Then I actually copied the previous version.
I think the UX could be improved a bit here. When the snapshot is 0B you could display text like “Nothing to copy to clipboard. This file snapshot is empty. Check other file versions” instead of “Copy to clipboard” button.
Or maybe we should not show the diff by default but just the whole file content of the snapshot. Then it would be cleared that this is actually empty snapshot.
This a just my random thoughts about improving the UX of recovery window.