Hello,
There was an outage with facebook this morning for about an hour. We highly recommend that you bind your account to prevent this issue in the future, as we cannot control facebook's login protocols nor guarantee service on their side.
Thanks and have a great day!

P.S. Here are the instructions to bind an account. It works both for google and facebook.

https://forum-narutoen.oasgames.com/page/show-post-54232-1.html