Editing Date fields through either FeatureForm or Editor widget is broken because the API treats a null value as valid date/number, even if the field is specified as required and has a RangeDomain. Docs: FieldConfig | ArcGIS API for JavaScript 4.14
This means that when creating a new feature the user can just "click through" date/number fields without entering anything (recorded as a null) (or if editing, deleting the existing values) and the API will accept this null value as valid.
Should FieldConfig support a nullable (boolean) option?