A Crepe Myrtle planted in July by a landscaper shows signs of stress. There is a gray/green scale on the bottom reaches of the main stalks. Also, many leaves have turned a dark green/brown color. However, the new growth leaves look normal.
Crepe Myrtle Health
Three things: 1) Some stress on newly planted trees is natural. 2) Go ahead and talk to your landscaper; it's my opinion that landscapers and plant stores should be held accountable for their work; a good landscaper would want to know that the customer is concerned. 3) Here are some articles on crepe myrtle that will give you some clues and point the way for the future: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/
PS: When it comes time to prune, if you have a landscaper do it, question them carefully about how they will be cutting. Make sure they're not a "crepe murderer!"