When a detecting region goes through a SWAP gate in both directions, it is shown to cancel out on the vertical bar of the gate
In a SWAP gate, this is mostly an incorrect interpretation; the channel in the middle of the swap gate supports 2 qubits of information rather than 1 qubit of information typically being moved vertically in 2Q gates (like CX or CZ), and so it is not the case that having Z sensitivity on both 'branches' of the swap gate cancels out the Z sensitivity in the middle of the gate
For SWAP and SWAP-like gates, the code coloring the vertical bars should follow more complex rules, and should color the bar if eg ZZ -> ZZ sensitivity through the gate
For example:
When a detecting region goes through a SWAP gate in both directions, it is shown to cancel out on the vertical bar of the gate
In a SWAP gate, this is mostly an incorrect interpretation; the channel in the middle of the swap gate supports 2 qubits of information rather than 1 qubit of information typically being moved vertically in 2Q gates (like CX or CZ), and so it is not the case that having Z sensitivity on both 'branches' of the swap gate cancels out the Z sensitivity in the middle of the gate
For SWAP and SWAP-like gates, the code coloring the vertical bars should follow more complex rules, and should color the bar if eg ZZ -> ZZ sensitivity through the gate