Dry soil conditions are usually the cause of browning on those plants. In a container the soil dries out quickly. Also the fact that the browning is on the front side would indicate perhaps more sun and thus more need for water. Feel the soil to get an idea how often to water. Keep the soil moist but not soggy wet. You might try turning the containers to give all sides a chance to get the sun exposure and give the affected area a little break from the sun.
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