Answer: Photinia, because it is a broadleaf evergreen, will naturally lose some of its older leaves during the year so what you are seeing could be a normal shedding process for your plant. If the dropping leaves are concentrated in the center and lower down on the plant, it's probably normal. You can encourage a thicker, denser growth habit by pruning your photinia each spring.
If the dropping leaves are the newer leaves, then I suspect your photinia is showing signs of transplant stress (complicated by weather extremes). You really can't help the process along other than to water your photinias deeply once each week. As soon as the roots become established your shrubs should perk up. Next spring you can prune them back to encourage them to fill out a bit.
Best wishes with your landscape!
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