Cannot logout from Facebook account problem

Installed Ytth social login and activated Facebook login. Login and logout were smoothly.
But a problem just happened in this two days.

Facebook Login has no problem. But then, I cannot logout from my website (even if I had logout from Facebook).
And, I cannot edit the account information inside my website and I cannot use another account to login my website again unless I use other system or other browsers.

May I have your help on this, please?
It is very urgent. Thank you very much.