PHP file_get_contents reading local file sometimes gives me empty string, but should always have something in it – CentOS

My centos cron-job code reads the local file and sometimes gets an empty string, but I never write an empty string to that file.

/*
 * in a cron job
 */

// verify that the file exists
if (!file_exists($my_file_path))        // if the file does Not exist
{                                       // then error
    error_log("file does Not exist");
    exit();
}

// read the file contents
$file_contents = file_get_contents($my_file_path);

// check result
if ($file_contents === false)           // if read failed
{                                       // then error
    error_log("file_contents === false");
    exit();
}

// look for empty string
if ($file_contents === '')              // if contents is empty string
{                                       // then check again after sleep
    error_log("file_contents === ''");
    sleep(1);
    $file_contents = file_get_contents($my_file_path);
    if ($file_contents === false)           // if read failed
    {                                       // then error
        error_log("file_contents === false, after sleep");
        exit();
    }
    if ($file_contents === '')              // if contents is still empty
    {                                       // then log it and exit
        error_log("file_contents is still empty, after sleep");
        exit();
    }
    else                                    // else contents Now Exists
    {                                       // so log it and use contents
        error_log("file_contents Exists, after sleep: $file_contents");
    }
}

In two places I write to the file:

// write the file contents
file_put_contents($my_file_path, time());

In one place I can remove the file (but I checked, and this code is Not being executed):

// remove the file
unlink($my_file_path);

I can’t see how file_get_contents should ever give me an empty string, even if it was being unlinked.