lsof php5 maxlifetime and sessionclean prevents laptop to suspend

My laptop (Lenovo T450s) fails to suspend sometimes with Ubuntu 14.04 LTS. I have checked the kern.log and found out lsof processes started by php5 package is causing a problem. The relevant section from the log file is attached.

Description: Ubuntu 14.04.4 LTS
Release: 14.04

php5:
  Installed: (none)
  Candidate: 5.5.9+dfsg-1ubuntu4.14
  Version table:
     5.5.9+dfsg-1ubuntu4.14 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
     5.5.9+dfsg-1ubuntu4 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

It seems to be unfinished accumulating lsof processes have a problem with mutexes, so Ubuntu can't pause them. I have the most recent BIOS version and everything is up to date.