Villagers in a naturally generated village keep walking off edges and taking fall damage. This makes them increase their prices. As far as I know, all mobs are supposed to avoid walking off drops higher than 3 blocks.
Here's a video of it happening when I was trying to trade.
Environment
CPU: AMD Ryzen 5 1600X Six-Core Processor
GPU: Radeon RX 480 Graphics
Java version "1.8.0_211"
Windows 10 Pro version 1803
Playing on a vanilla SMP server.
Duplicate of MC-151810. Feel free to add your video to that report.