Steven, this needs to check the class of the form why it changed the structure or layout. You can contact CK at help@convertkit.com24 to check this. Can you check if you use JavaScript, HTML, or Ck plugin when you embed this to your website?
You can try to add this CSS code as well.
.formkit-background {
min-height: 300px !important;
}
https://help.convertkit.com/en/articles/2502480-custom-css-for-the-form-builder16
If that doesn't work contact Convertkit.