So the wall does have damp coursing, and the problem is not water wicking its way upward? What about on top of the wall, is it under a roof, or if a parapet wall, is the parapet top of the wall adequately sealed? The reason why I ask is because it is rare (in my experience anyway) that a proper outdoor acrylic paint in a vertical application is penetrated by water.
Then again you did say that the paint cracks and that water penetrates the cracks. Does it crack along the underlying brick and mortar pattern, or is the crack haphazard / random?