Sometimes it may happen that admin is not able to save any added fields in the vendor registration. It may happen that there is some database issue. This can be easily resolved , by adding the below code in the functions.php file of your current active theme the issue on the database will be fixed –

add_action('init', 'fix_mvx_reg_issue');
function fix_mvx_reg_issue(){  
delete_option('mvx_vendor_registration_form_data'); }

Once you’ve inserted this code, simply refresh the registration settings page. Following that, feel free to delete the code from the functions.php file