Samurai Search release V1.19 includes a resolution of the issue of partial downloading of files associated with an iCloud search folder. However, there is an implicit limitation relating to iCloud.

When an iCloud folder is updated on one of your devices, the changed metadata is propagated quickly, and it is this metadata that allows the detection of and subsequent downloading of the file. However, if the network is slow, or the upload of changes hasn’t completed, Download iCloud Files will only download what is currently available.