Hi @HanLu1 ,
When you set required="on" inside a nested multifield item in a Content Fragment Model, AEM only evaluates the validation rules during the model editor’s initial load.
That’s why the Must-fill message appears only after a page refresh because the Coral UI components are re-initialized at that moment.
This happens because the child input (inside the multifield repeatable block) is added dynamically, but the Coral validation API is not re-applied automatically after the “Add” action.
You need to make sure the Coral validation is re-initialized every time a new multifield item is added.
A simple clientlib with a small JS snippet can solve this.
Hope this will helps you 🙂