Aurinia saxatilis 'Basket of Gold' can get crown rot, especially if grown in rich soil even if the drainage is good.* It also prefers neutral to acidic soil, so if the wall is limestone, that could cause a problem as limestone is akaline.
Soil mealybugs are also a possibility.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.