Good photos, and I think it is some sort of fungal disease as I can see little pustules around some main spots, plus the orange colour which makes me think of some kind of rust infecting the leaves. Thing is, I am no expert on this, but know that certain types of plants are prone to their own specific type of rust, such as rose rust, hollyhock rust, leek rust, and probably many more examples of this can be found online. To my knowledge, rust is an umbrella term for various specific types that will only target plants they have a propensity for and only when the weather is right. You can't do anything about the weather conditions that promotes rust, but don't think it will go all over your garden! Having said this and looking at your original post again, you only noticed the orange spots on certain weeds and not on your plants. The spots on your lavender and Magnolia may still be due to the sun on water droplets, as they tend to be a brown colour rather than orange, or it may just be a form of mildew which shouldn't affect the plants if well-established. I've just gone out to look at my one and only lavender whichhas no spots on its leaves, but that's nothing to go by. Personally, I wouldn't worry about the weed rust (if that's what it is and not knowing the type of weed) going onto your other plants. As I said, they are species-specific, but just goggle lavender and Magnolia to see if they have their own species-specific rust.