I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
It is most likely due either to a soil problem (dry periods, soggy wet conditions, excessive fertilizer salts) or to a leaf fungus (usually promoted by wetting the foliage). I suggest you watch the soil moisture levels carefully, make sure the plant is in adequate lighting and trim away any damaged foliage. Fertilize it lightly with a soluble plant food at the low constant feed label rate if it has not been fed in the past few months.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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