Circular dominance is a rather common phenomenon in Go, even amongst strongest pros.
In the simplest constellation, there are 3 players A, B, C, where A usually beats B, B usually beats C, and C usually beats A. All three players may (but need not) have the same rank.
Such "winning loops" may be caused by differences in styles and skill profiles between the involved players.
The easiest example for circular dominance is the game of stone-scissors-paper.