When redirecting a form with a redirect input, for example

<input type="hidden" name="redirect" value="<url>">

the browser may preserve the window hash after the redirect. For example, submitting

<form>
  <input type="hidden" name="redirect" value="my-other-page">
  <button type="submit">
</form>

from mydomain.com/my-page#my-hash may take the user to mydomain.com/my-other-page#my-hash.

That isn't always desirable; for example it isn't uncommon to need to redirect to the top of another page, where a confirmation message may be shown. To do that, take the hash out of the current page before submitting the form:

myForm.addEventListener('submit', () => {
  window.history.pushState(null, '', window.location.pathname)
}

now submitting the above form from mydomain.com/my-page#my-hash should reliably take the user to mydomain.com/my-other-page.