Have these been exposed to cold temperatures? If not then I could suspect a fungal problem which can happen if they remain too wet for too long. Can you include photos? This might help me to help you better. For now here is an article on the care of the rubber plant: https://www.gardeningknowhow.com/houseplants/rubber-tree/how-to-care-for-a-rubber-tree-plant.htm
Answered on February 26, 2019
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