Data is capturing incomplete when submit by different user at a time

Created HTML form but when submit the form ata time by two defferent users its capturing incomplete data like few data showing as blank in first submit and second submit its caprturing all the informations. Need you assitence how to prevent this issues.

<script>
  // Prevent forms from submitting.
  function preventFormSubmit() {
    var forms = document.querySelectorAll('form');
    for (var i = 0; i < forms.length; i++) {
      forms[i].addEventListener('submit', function(event) {
      event.preventDefault();
      });
    }
  }
  window.addEventListener('load', preventFormSubmit);    
     
     
  function handleFormSubmit(formObject) {
 google.script.run.processForm(formObject);
 
     
   }
 
 
 
 
</script>