This can be replicated by placing a Grottoceratops on a slope of one-block high steps. If one attempts to tempt the Grottoceratops with a Tree Star, they will look at you and follow you perpendicular to the slope, but not be able to climb down. They appear to be better at climbing up than down, leading them to inevitably get stuck somewhere if a chunk is loaded for long enough.

Mod version: 2.0.2
Minecraft version: 1.20.1
Platform: Mac OS