LimeSurvey version: 6.6.7
Own server or LimeSurvey Cloud: Own server==================Since today, my respondents can no longer access my questionnaire. They keep getting the infamous "Whoopsie, session has expired" message.When I tried to log in to my account to check what was going on, I noticed that LimeSurvey wouldn't let me in at all. After entering my credentials correctly, I am redirected back to the login screen without any error messages. In fact, even when I enter incorrect credentials, LimeSurvey doesn’t display any warnings—it simply refreshes the login screen.I have already tried clearing my cache and testing on different devices and browsers, but without success.I also checked my configuration file on the server, and the session expiration time is set to the default (2 hours). I have never modified this file or any other configuration settings.What could be causing this issue? I have already checked my web server, and everything seems fine. I'm running LimeSurvey on a PHP 8.1 server. The web files were uploaded via SFTP. LimeSurvey has been working perfectly for months until now.Additional note: The survey I was working on was quite long—around 71 questions. This is different from my previous surveys, which were usually much shorter. I’m not sure if this could be related to the issue.

Maybe you session directory issue.
Check you php error log.

There must have been any changes. And this doesn't sound like anything Limesurvevy related. And if you didn't change anything on Limesurvey (update/upgrade) there is no reason for Limesurvey suddenly change behaviour. So you need to check if something happened on your server.

Like Denis said, have a look at the session folder. Maybe it is full, maybe the sessions are not deleted automatically. But this sound like a server issue, rather than a LS issue.