This function works if you click "remember me". It doesn't work when you log in normally or log in via social networks.

Is it possible to set the "remember me" checkbox for entering social networks in wpdiscuz? After closing the browser, the login is reset.

The registration is handled by WordPress side. As far as there is not the "Remember me" button when you're logged in via social network it doesn't keep the users logged in. 

Please note: It doesn't create multiple user with the same social account. I.e. when you first time logged in via FB with your account it'll create the new user on your WordPress site, when you second time logged in via the same FB account it'll not create a new user anymore, as far as the account is created. 

I may suggest you tray the solution provided her. It may be helpful for you: http://wpcodesnippet.com/keep-users-logged-in-longer-wordpress/#:~:text=By%20default%20WordPress%20keep%20users,you%20to%20re%2Dauthenticate%20again