How to remove re-execution of form_alter for DRUPAL8?

Question

Drupal

Created a contact form. When you click "send", there should be a record in the database of data from the fields. Some of the fields are filled in automatically by hook_form_alter before the form is displayed.
For these purposes, I wrote a function in $form['actions']['submit']['#submit']... form.
Why is hook_form_alter suddenly re-executed? How to bypass it?