Consider the following ZX graph:
If you perform tensor contraction on this graph, you get the zero tensor. Therefore it should be equivalent to this graph:
How do you rewrite the graph, axiom by axiom, to get from the attached loop to the independent node?
What I do know how to do is to pump a $\pi$ node and some scalar factors out of the loop. This is enough to e.g. make PyZX simplify the graph into different results depending on which rewrites I've applied to the graph: