CodeIgniter session expires randomly

Question

I am using CodeIgniter 4 for my websites, and has the following session settings in the .env file.

app.sessionDriver = 'CodeIgniter\Session\Handlers\DatabaseHandler'
app.sessionCookieName = 'ci_session'
app.sessionExpiration = 86400
app.sessionSavePath = 'ci_sessions'
app.sessionMatchIP = false
app.sessionTimeToUpdate = 300
app.sessionRegenerateDestroy = false

However, the session always expired much earlier and randomly.

I have also try setting sessionExpiration to 0, but this does not solve the issue.

Please help.

Thanks in advance.