Can't login any more when SuperCache runs

Well. It worked for a few months now with only minor issues, i.e. one sometimes had to login twice, but most of the time the first login was successful. Wasn’t sure who was the culprit then.

Now since yesterday (and there were NO updates of any plugin or WordPress made) one couldn’t login anymore at all. Well, you can login (no error message) but I don’t see the Dashboard or so, just the same page with the login in the sidebar.

I have now proven that

– if I cannot login
– and remove the supercache-directory from plugins
– i can login immediately

(and reactivating breaks the login again).

Maybe this is a specific setting I am using?
The debug output lists something like

09:40:05 /pbc-wp/wp-admin/admin-ajax.php In WP Cache Phase 2
09:40:05 /pbc-wp/wp-admin/admin-ajax.php Setting up WordPress actions
09:40:05 /pbc-wp/wp-admin/admin-ajax.php Not caching wp-admin requests.
09:40:09 /pbc-wp/wp-admin/admin-ajax.php wp_cache_get_cookies_values: /^wp-postpass|^comment_author_|^wordpress_logged_in_0661e647cd2f543da4e775fcb2ce5aba/ Cookie detected: wordpress_logged_in_0661e647cd2f543da4e775fcb2ce5aba

for a login request. Any ideas?

https://wordpress.org/plugins/wp-super-cache/