Mealybugs are tiny enough and hardy enough that they can hide for months in the tiniest crevices outside the pot. So if you put a healthy plant where an infected plant once was without treating the surrounding area, you will have mealybugs again.
A deep clean of the surrounding area (tabletops, saucers and pot outsides, placemats... anything within about 5 ft ) and a systemic are my weapons of choice.