Loginhttps is not recommended. Unfortunately cookiesecure will not work with loginhttps on, because only the login will be served over SSL, not the rest of the user's session. So secure cookies cannot be used. Even if you set cookiesecure to on, it will be switched off automatically. We need to improve this and add an explanation in the help text as to why that is.
But the plan is to remove the option and just have it automatic when you are using full https. https://tracker.moodle.org/browse/MDL-55662
I think the only way to solve this is to turn loginhttps off and go full HTTPS.