Problem with rafter / roof overhang exterior painting

Hello,
the roof overhang (rafters and boards) of the newly built semi-detached house was painted about 4 years ago with white Venti Satin lacquer from the company Südwest and has shown black spotting on the white lacquer for about 1 year - see attached pictures.

The following questions:
1.) Was the wrong white lacquer used, not weather-resistant etc.?
2.) What could the black spotting be - weathering, algae etc.?
3.) What is the appropriate procedure to fix this? Sanding and repainting?

Best regards,
Michael

1) The color could have been better. Was the insulating primer forgotten? 2) Weathered, ingredients of the wood have come through. 3) repaint, loose paint off, otherwise sand, use Consolan.

Thank you for the info, I cannot say whether [Isoliergrund] was used. The wood should have already been pretreated by the master carpenter. And the plasterer applied the final coat with the white varnish. Could this still be a warranty case after 4 years?

Here you can see the white pretreatment by the master carpenter on the roof overhangs before they were painted with the white paint Venti Satin.

No. No warranty. That was just window paint, it doesn't give more. Primer is used to prevent resin from softwood, etc., from bleeding through the paint, which is always visible with white paints. With red or brown you skip it, with gray, unless it’s shark grey, you do too. The paint Konsolan that I recommend works differently; it soaks deeply into the wood and grips. That would also work with paints, but then the first coat has to be heavily diluted. Who still does that today! Too expensive, too time-consuming. Just smear it on and that’s it. The customer doesn't want to go broke over a few boards.

Did you take the pictures at my place?
It looks the same to me. As long as it doesn’t really cause damage, I won’t do anything for now.