There could be several reasons why your XenForo 2 admin login keeps expiring, such as incorrect server time or a browser issue. Here are a few steps you can take to fix it:
- Ensure that the server time is correctly configured in the system settings.
- Clear your browser cache and cookies, or try using a different browser to see if the issue persists.
- Disable any browser extensions that may be interfering with the login process.
- Check if any server-side security software, such as mod_security, is blocking the login request.
- Try resetting your admin login credentials or restoring a backup of the XenForo database.