See FormStructureTest.ParseQueryResponseAuthorDefinedTypes

The inferred AutofillType is UNKNOWN_TYPE when the server_type (or the autocomplete attribute?) is password-related. Not having a proper AutofillType could lead to problems in other logic (https://codereview.chromium.org/2003563003 fixes an issue where autofill would be affected when an autocomplete type such as "new-password" was specified).

Please have a look and see if there is a user impact.

Easily reproducible with such a form and enabling chrome://flags#show-autofill-type-predictions:

<form name="np" id="np1" action="https://example.com" method="post">
  Name: <input type="text" name="firstname" /><br />
  Phone: <input type="text" name="phone" /><br />
  Password: <input type="password" name="password" autocomplete="password"/><br />
  <input type="reset" value="Reset" />
  <input type="submit" value="Submit" />
  </form>