What @postwick tried to say is that if you go to a deep level, those activities, will never run in parallel, instead you can imagine it as the bot switching continuously from A to B, and then back to A… super fast, until both workflows reach the end, is like if the active point keeps changing from parallel path to parallel path, simulating this “parallel” action
Using Step into, since you’re stopping the activity from doing this “fast” changes from A to B, seems that the parallel activity is not working, but it’s because the changes from A to B, are currently slower