anyone else find cleaning mold off walls harder than it looks?

It's harder because on a painted plaster or drywall wall you're often only cleaning the surface while the stain sits in the paint film. Wipe with detergent and water (wet, never dry brushing, that just spreads spores), dry it properly, and if a shadow is left, a stain-blocking primer before you repaint. The real fix is why it's there. A cold outside wall behind furniture with no airflow is the classic spot. Pull the wardrobe a few inches off the wall and it often stops.