Plaster reacts dramatically to the environment, specifically to moisture. This is a phenomenon seen in both very old homes (using lime plaster) and mid-century homes (using gypsum lath).
If your cracks appeared shortly after the job was done, the culprit is usually the application process. what causes plaster to crack
If you see cracks that are wider at the top than at the bottom, or cracks that run in a "stair-step" pattern along mortar joints (in masonry) or diagonally from door frames, this may indicate a shifting foundation. As the ground beneath the house expands or contracts (often due to soil type or heavy rain), it puts immense pressure on the walls. Plaster, being brittle, is the first material to snap under this pressure. Plaster reacts dramatically to the environment