Unable to reproduce issue on our current dev version of ArcGIS Online. Also, the default values for fields are what will display if the user does not provide their own values. Therefore, it is not necessary to already populate those fields in the form as if they are required fields and set values. The blank form fields make it more likely the app user will supply their own values when submitting an entry. And if they don't, the default values will be supplied. If it is desired to have something in the form's fields on load, it is suggested to use hint text.