Leaves falling off? ? ?

I an growing a tea olive -- osmanthus fragrens -- in a pot. This is supposed to be an outdoor plant that grows 12 feet or more, but it's pretty much confined to the deep south.
My bush endured for several years in a large pot, but finally died. So I ordered a new one, which came in a small pot. It seemed quite healthy when it arrived, but a month or so after I replanted it in a larger pot, leaves began to fall off.
Any ideas about what's causing this, or what can be done to prevent it, will be most welcome.
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Older leaves? Younger leaves? Color changes? Spots?
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