this is a solution tested and running ok.
(PD: The solution seems to be the use (or abuse) of the @ to avoid the warnings, and I am not sure if this can be considered a real solution or not)
Script called on form display:
$inputCookie = JFactory::getApplication()->input->cookie;
$bdayd = $inputCookie->get('rsformdatabdayd', '');
You have posted snippets that are using two separate means of updating the form.
For one, you are declaring:
This means that the rsformdatacountry cookie value is a string (not an array). This is appropriate assuming that your form is not allowing multiple selections.
When you call it, use:
$activeCountry = $inputCookie->get('rsformdatacountry', '', 'string');
The error messages appears to be for fields that you have not provided a value for in your "Script called on form process:" such as adress-level2 so I expect that com_rsforms/helper/field.php is expecting a value in an array, like the other fields you do provide, but you are giving it an empty or no value at all.