A few possible issues I can think of off the top of my head. Both rhodies and laurels (Prunus laurocerasus) like at least part sun, and the laurels are happy in full sun. So light levels are an issue since between the building and the trees this looks like fairly dense shade.

Maple trees have dense roots that do a good job of sucking up moisture and nutrients. Unless you are watering and fertilizing the entire maple's root area, you have a new shrub trying to compete against an established maple and the shrub is losing. The established shrubs have better root systems and so manage to hold their own.

Is it close to a masonry foundation that might be creating alkaline soil conditions?

Have you considered an ornamental pot to give height planted with annuals or hardy perennials for that spot?

Have you had a soil test done for basics like pH? Or are you just shooting in the dark with the amendments?

Looks biological to me, as in a water mold such as Phytophthora or other blighting condition. What's that thing to the right of the shrub? Not a bird bath or fountain, is it?

I'd look for wetness in the soil, check for signs of pathogenic activity like rotting of the roots or Armillaria rhizomorphs on the crown.

Also since you are in the States there should be a USDA Cooperative Extension branch office you could try taking samples to for analysis and comment, if you can make it during their open hours.