DEV vs. PROD Behavior for Non-Mandatory “Classrooms” Field

Hello,

In the Learning module, on the “Add activity” page, I made the “Classrooms” field non-mandatory, via page composer. I published my Sandboxe, did my tests and it worked, the field became non-mandatory and you could submit without filling it in. =⇒ All these tests were performed in DEV
After validation by the customer, I made the same changes in PROD, made the “Classrooms” field non-mandatory via page composer and published my sandbox. Then I ran my tests, result = KO. The system gives me an error saying that the “Classrooms” field is mandatory.
Can you please help us? Why does it work in DEV but not in PROD?