So let me explain to you what my first script does. The code is triggered, once you set the NEW value into the assignment group. It checks the following:
IF the new value of 'Assignment Group' is different than the old value (the one was there when the form is loaded) AND the 'State' field is 'Open/Work in Progress/Pending' then it makes the 'Work notes' field mandatory. Please NOTE: if you changed the assignment group, set the status to 'Open/Work in Progress/Pending' and the work note became mandatory, then IF you do not submit the for but try to change the state to not of these there above (let's say 'Closed complete'), then, OF COURSE, the work notes will REMAIN to be mandatory because the 'Assignment group' is still other then it was when the form is loaded.
You cannot expect the 'work_notes' field to be set back to the optional if you change the state to another one BUT the Assignment Group field contains the new value. You have to save the ticket and afterward change it to the new state. The client script is constantly checking the assignment group field. This is its nature, otherwise, you can't control the change of assignment group field. I hope it now finally makes sense.
