My opinion is that mold means moisture, and if the mold came back after you bleached it before, perhaps your drainage isn't quite as good as it could be. We have one house we own that perennially has a problem with a light covering of green mold on the north side of the house - all outside, mostly on the windowsills but occasionally even on the sidewalk or brick wall and even in the very flat or slightly-tipped-towards-the-house lawn, where it is shaded almost constantly. Nearby, my old house also has a north side that is almost always shaded, but no mold. I think the lawn slopes ever so slightly away from the house and that helps moisture dissipate.

My own current house's north facade has never had mold issues (knock on wood), and I live within a mile of the first two houses but I also have gutters and french drains that help direct water away from the house, even though my backyard slopes down towards the house.

So those would be my suggestions - check slope of your yard, add drainage in the form of French drains and/or gutters. Otherwise I think you will be constantly fighting it if you don't address the root cause.

I read somewhere that white vinegar kills mold better than bleach, so you might try that quick fix until you can put Mia's plan into action.

Thanks.