A tip: keep your nodes more organized in the flow they go. Keep the lines going one direction and it's easier to diagnose problems.
The problem is recursion. You are trying to connect your tone curve to a component that affects the tone curve. if you trace the line from the component you're trying to plug it into, it goes back to the tone curve itself.
To fix this, plug in a different component to "A-Variance" on the tone curve that isn't affected by what you're plugging it into.

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