error_log appearing even though debug mode is off in wp-config.php

Yesterday I deleted the error_log in performanceconsultants folder because it allows public to view information such as the file structure on our website. The file appeared again today with these errors (I replaced folder names with XXXXX):
[09-Mar-2017 00:45:56 UTC] PHP Fatal error: Maximum execution time of 30 seconds exceeded in XXXXX/wp-includes/option.php on line 0
[09-Mar-2017 06:45:54 UTC] PHP Fatal error: Maximum execution time of 30 seconds exceeded in XXXXX/wp-includes/wp-db.php on line 1877
The debug mode is off so I'm not sure which plugin is causing the errors or what the errors mean.
Line 1877 appears to be blank. I think that line 1885 is } and line 1886 is also } so perhaps the second } needs deleting but I wouldn't want to change something I don't understand!