Plaster facade WDVS mineral wool brown stains

Maybe like with screed where contaminants also lead to brown stains
These are usually organic residues (wood, etc.)
Maybe here too?

I just did an inventory again: there are 19 spots, with the majority on the north and fruit facade.

Is there any progression or has the effect come to a standstill?

I would absolutely not accept partial removal, you can always see that. You can do that for a single missing spot because the effort would otherwise be disproportionate, but with 19 spots the case is clear.

I would, if it comes to the point that everything is to be painted, first definitely paint one spot. Not that the whole house is painted and then it blooms through again.

Apart from the brown stain on the window lintel, the other stains rather seem to be related to the filling of the holes for the scaffold anchors. Rain can also run into the ETICS along the scaffold anchor – so moisture may have partially accumulated there. The plugs for the anchor drillings in the ETICS are usually properly installed by the ETICS company. Sometimes, however, the scaffolder takes care of this during dismantling using his own plugs. Whether the materials are compatible may only become apparent later. This should be checked.

Aside from the brown spot on the window lintel, the other spots rather look as if they are related to the filling of the holes for the scaffolding anchors in

That would be so obvious that the plasterer should have noticed it. I would suggest the building component opening at a spot that is not visible.