I have tested with a similar workflow in my end and it works properly. The only difference is that I do not use current Item: Assigned to in the people field. And please remember to log the outcome variable value before the if condition.
As there is a setting in the task action "Default Outcome", have a try to set it to rejected and try again. If it always goes to FL Review Stage, it means the task is not properly completed by user. Have a test to set the task with a certain user.