I guess this is one of the Syzigium species. Brush cherry is just one of the common names and can apply to a number of different species.
They should be evergreen so dry leaves is not good.
Dry or cold can both cause similar symptoms. My area is marginal for these with temps dipping just below freezing through winter so they sometimes drop leaves here. The good news is these are pretty hardy and often recover after unplanned defoliation.
Make sure they have enough soil moisture, keep above freezing and cross fingers.
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