Buckling

Root Cause - Moisture.

When wood flooring buckles, it becomes separated from the subfloor. Buckling is usually, but not always, accompanied by cupping and swelling.

Crowning

Root Cause - Sanding prior to complete aclimation.

"While it is theoretically possible that excessive moisture could cause crowning, it is more likely that the floor cupped and then was sanded flat before it could dry and flatten on its own."¹

¹ NATIONAL WOOD FLOORING ASSOCIATION TECHNICAL PUBLICATION No. C200 © 2002

Cupping

Root cause - Moisture

Have you seen this issue in your hardwood floors? It's called 'cupping' and it's common. The occurrence is created by an imbalance of moisture in the wood. In this case, as in most I inspect, the contractor did not sufficiently evaluate the job site conditions prior to installing wood floors, creating a situation where moisture is introduced to the floor.
Floorensiks by Craftcare

Abnormal Gaps

Root Cause - Prior exposure to extreme moisture

Gaps in the floor that remain with seasonal change.

Chatter Marks

Root Cause - Faulty Sanding Equipment

Consistent sanding imperfections across the grain of the wood varying from ¼ inch to 1 inch apart.

Greenhouse Effect

Root Cause - Inadequate Ventilation

Floors in a vacant house that shrink or swell due to inadequate ventilation (which leads to abnormal levels of humidity).