Customers cannot login to my website. Every time some logs in, the page simply refreshes and nothing happens.
As far as I checked, it could be a problem with session files. In my local dev machine, I can see new session files generated in <magentoroot>/pub/var/session every time someone logs in.
However, in the production server, such files do not exists. Instead, a new one is generated at /var/lib/php/sessions every time someone tries to login unsuccessfully. I also could not login to my admin page last night (which generated one session file in /var/lib/php/sessions per unsuccessful login). But after I went to bed I am now able to login to my admin page again (which keeps 1 session file for admin login in /var/lib/php/sessions). The customers are still unable to login however.