When creating a new subscription in serials the "first issue publication date" field is not required. It is not a problem when it is left empty for libraries who don't do serial receive and don't need Published on and expected on dates to work. But libraries who do can create a subscription without filling this field and run into problems because of this. Since this information is available to all libraries, making it required won't break the function for anyone, but could enhance usability.
The first issue publication date is required now.