Persisting login cookies if the user didn't explicitly consent to data collection is specifically _not_ exempted by ePrivacy. To quote a EU Working Group's opinion on this: 'Persistent login cookies which store an authentication token across browser sessions are not exempted under CRITERION B. This is an important distinction because the user may not be immediately aware of the fact that closing the browser will not clear their authentication settings. They may return to the website under the assumption that they are anonymous whilst in fact they are still logged in to the service. The commonly seen method of using a checkbox and a simple information note such as “remember me (uses cookies)” next to the submit form would be an appropriate means of gaining consent therefore negating the need to apply an exemption in this case.'

You can find the full opinion text here https://ec.europa.eu/justice/article-29/documentation/opinio...