Interesting scenario that may help someone else out. No technical details/explanation and instead just a push/clue in the right direction.
The scenario: remote automated creation of a User Account based on a successful/VERIFIED IPN PayPal Transaction. Mysqli Query creates user and usermeta data, but the value of that data contains hidden formatting characters and invalidates usage of that data called in Form processing. Very simple solution without changing/altering any existing DB Tables. Basically this ensures that your data is only ASCII printable characters and even using $mysqli->set_charset("utf8"); is not really that important since you are preparing your data to be processed and inputted "ASCII clean".
$create_ipn = $mysqli->prepare("INSERT INTO xxx_somewhere (some_ipn_parameter , email, domain, item) VALUES (?, ?, ?, ?)");
$create_ipn->bind_param("ssss", $some_ipn_parameter, $email, $domain, $item);
$some_ipn_parameter = preg_replace( '/[^\x01-\x7F]/', "", 'the_actual_ipn_data' );
$email = 'edward@ait-pro.com';
$domain = '';
$item = 'Test';
$create_ipn->execute();