GaiaCookieManagerService randomly ignores some cookie changes notifications:

See:
https://cs.chromium.org/chromium/src/components/signin/core/browser/gaia_cookie_manager_service.cc?rcl=17145a3a105605a589b47b881d51fa0277f899dc&l=684

  // Ignore changes to the cookie while requests are pending.  These changes
  // are caused by the service itself as it adds accounts.  A side effects is
  // that any changes to the gaia cookie outside of this class, while requests
  // are pending, will be lost.  However, trying to process these changes could
  // cause an endless loop (see crbug.com/516070).