How to embed subflow in a flow for one time run

Hi, I have a subflow B
sub1 -> sub2 -> sub3 (return to calling)

I have a main flow A. I want to run B somewhere in the middle and then continue A.
node1 -> node2 -> SubFlow B -> node3 -> node4 -> … end

At the end of B (sub3), I have selected “Return to calling node” transition. With that, it always returns to node2 in main. And in node2, it goes straight to evaluating transition conditions, rather then executing the whole node including OnEnter and OnReceive. The condition evaluates to true and it transitions to SubFlow B again. And this loops endlessly.

All I want to is to run the SubFlow B once. Like calling some method of another class. How can I achieve that?