We can't tell from the photo exactly what the issue is.
Overwatering and underwatering can look similar.
It will take some sleuthing- things we'd consider include:

• how deep is the mulch layer? (remove any more than about 3" and keep it pulled back from contact with the trunks/stems/crowns of plants).
• did the soil seem the same when you dug that hole?
• look for signs of any gnawing of the wood on the lower part of the plant and gently tug upwards to see if, by chance, it has been chewed underground by voles (not moles, which only eat worms, grubs, etc.)

At this point it's serious enough that it's worth popping it out of the ground carefully to look at the roots and soil within the hole. What color are the roots? Is the hole holding water? What else do you see? 

We can't be sure but the plant is stressed to the point that it may not recover, but you can wait and see.

Is the plant under warranty from the seller? If so, consider replacement. 
Making sure too- the plants you have there are shade-lovers- they'd like some morning sun but won't do well in full sun.
Also, it's difficult to tell from the angle, but they look like they are planted pretty close to the house. Read the tags for both the Pieris (Japanese Andromeda) and Cherry Laurel to see how large they are expected to be at maturity and re-plant them if needed, taking that into account.


Christine