I’ve heard designers use these words as though they’re interchangeable. They’re not.

Consistency (n): 1) conformity in the application of something, typically that which is necessary for the sake of logic, accuracy, or fairness, 2) the way in which a substance, typically a liquid, holds together; thickness or viscosity

Coherence (n): 1) the quality of being logical and consistent, 2) the quality of forming a unified whole

Consistency can create coherence. But thoughtless, overly rigid consistency can create incoherence. For people to successfully derive meaning from an information environment, the environment must be coherent above all — even if that calls for some inconsistency.

Aim for coherence.

(Definitions from the macOS Dictionary app.)