I'be been monitoring the machine for some time and that we get frequently but randomly

Fatal error: Maximum execution time of thirty seconds exceeded in preprocess.php online 3.

The file appears like this:

ini_set('memory_limit', '128M');
@ini_set('session.bug_compat_warn','off');// php version installed on the server has a compatibility bug

What is the reason?

Look at your php.ini apply for max_execution_some time and try altering it inside

What goes on if you use because the time period limit? So that as another person pointed out, look at your phpinfo() output.