Though I can't rule out a potential bug, I've tested the game on my end and the area expansion seems to be working as intended (or as much as it should) -with a bonus expansion for the player in the attacking position (starting with the ball).
I appreciated the feedback, sorry for the inconvenience.
I tested it on a different browser. It seems this bug only happens when playing on Firefox. I guess that’s not really fair to judge you for that as I have also noticed unintended behavior when playing my Godot games on Firefox. I will edit my initial message to reflect that. Sorry for the confusion.