PDAF = Phase Detect AutoFocus
The latest and highly dubious trend with digital sensors is adding special pixels on the sensor to allow phase detect autofocus. These special pixels don’t come free: they invariably lead to image quality impacts of the kind that either must be suppressed (as with the Nikon Z7 and other cameras), or let alone to pop up in the wrong image—see for example Sony A9: Two Examples of Pattern/Banding Noise at ISO 100 (Pine Creek Skyline, Mt Tom).
This page shows troublesome pattern noise in a good exposure. The Fujifilm GFX100 cannot capture some shades of blue sky without visible pattern noise, due to the inclusion of its PDAF pixels. Whether or not is shows up and is a problem depends on various factors—but it is there and may defeat desired processing.
Yikes. I can’t see using the GFX100 for high quality landscape shooting in black and white—the chance of severe problems in the sky is a show-stopper. And... it's visible in color too.
I don’t have a good 'read' on how often the striping is an issue, but I’d bet it is a problem most of the time with blue sky if one wants to make compelling black and white landscapes. And it subtly problematic in color at times. It seems to depend on the shade of blue sky but it also cuts through other colors, as shown.