Are you also using any cache/CDN? Are you using the Latest version? (22 February 2022 V3.3.1). I've just tried to look more into the settings for the script on the demo. It doesn't allow me to look into the settings page, so I cannot see what options the script has.
It sounds like you need to set the cookie expiry and/or to a higher expiry time. If the session() expiry is not set then it will log the user out. Upon logging in (
https://ovoo.spagreen.net/demo/v33/user/do_login) the cookie:
ci_session is set.
You need set/extend the expiry for the cookie: ci_session. Perhaps digging further into the config file, other php files or settings you may find something to do with cookies and ci_session.
Codeigniter uses the same cookie.