I recently started using a Fuji GW490 with Portra 400 film. Having got the film developed, some of the areas out of focus (or smooth gradient areas) appear to have a 'splotchy' pattern of lighter dots that doesn't necessarily look like normal film grain. Perhaps the film is underexposed/expired? Possibly it could be how the lab handled it as I had a few other rolls come out fine.
I scanned using an Epson V600 with Epson Scan software, 48-bit TIFFs.