Hi Jeff, are your images particularly large or do you make a lot of changes which you save to the original file as part of your workflow?
The CPU usage is almost certainly from us uploading JPEG previews not the Smart Previews - particularly during develop edits as these force new JPEG previews to be sent from Lightroom desktop, but would not force new Smart Previews (unless the develop edits are modifying the original file making us think the Smart Preview is out of date) to be sent.
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Guido