Impossible to make 3 fields non-mandatory in the “create an activity” task

Hello,

On the “Create an activity” task, I made 3 fields non-mandatory via page composer “start time”, “end time”, “classroom”.
When I went to do the test afterwards, the star indicating that these fields are mandatory had disappeared. However, when I click on ok to create the activity, I get this error (view screenshot attached (it looks like the fields are still mandatory).

Thank you in advance for your help