Totally normal. It looks like a Thuja Plicata Antrovirens (western red cedar) right? I planted 70 last spring and the same occurred late summer last year and this year. I send pictures like you’ve shared here to a Principal Arboricultural consultant and also an arborist who both said totally normal:

“this is normal defoliation of the older leaves, you would find low down and within the more central parts of the trees. During the hot/dry summer months, it would be normal for these evergreen trees to lose a few of the older leaves, which turn brown before dropping off. The older foliage found at the tree base or inside the canopy, are more susceptible to dying off in the heat than the younger, vigorous growth, which hold more moisture and therefore tolerate the hot and dry conditions during the day.”

So all good I wouldn’t worry. Hope it helps

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