This sounds like a fungal infection. This can happen from time to time. You may think about repotting into fresh soil and then treating it the next time that you water. Just replace 1/4 of the water in the container with peroxide, and water once with that. This will usually clear up an infection in houseplants.
This article will help with the care of these: https://www.gardeningknowhow.com/houseplants/schefflera/schefflera-plant-care.htm