Frequent Session Timeouts v7.5.3

I recently upgraded my production instance to v7.5.3 and since then, users have been unable to login on Monday mornings - being met with this error message at login:

You have been logged out because your session has expired.

Since this is happening only on Mondays, I suspect it may have something to do with sessions timing out over the weekend. At the moment my only solution is to restart Apache. Is there something I need to increase in the php.ini file or has something changed in v7.5.3 that could be causing this? Thanks.

PS. All users authenticate via LDAP (MS Active Directory) - not sure if that makes a difference.