This plant...
Has developed some small white growths on it:
What is this stuff? It looks pretty foul. I did look up mealy bugs on Google Images, but those photos look different.
Looks like either scale or mealybug infestation - mealybugs are just a soft bodied type of scale. Check the undersides of the leaves to see if there's anything there that shouldn't be. You could probably wipe off the ones on the stems, and any on the woodier stems can be cleaned off using a cloth moistened with isopropyl alcohol or methylated spirits. Otherwise, you can try neem oil spray or insecticidal soap spray, but you will need to repeat treat if you choose to use these. Alternatively, choose an insecticide that treats for scale/mealybug. If you spray, do the whole plant, including under the leaves and all the stems. https://homeguides.sfgate.com/schefflera-pests-26994.html