I found this in the admin/autoupgrade folder error_log.
[16-Mar-2019 09:51:15 UTC] PHP Fatal error: Class 'Tools14' not found in /home/xxx/clone1.xxx.com/Admin/autoupgrade/ajax-upgradetab.php(51) : eval()'d code on line 1
Many lines with the PHP Fatal error. As each one is displayed the time is incrementally increased all the way to 10:39:49 UTC
[16-Mar-2019 10:39:49 UTC] PHP Fatal error: Class 'Tools14' not found in /home/xxx/clone1.xxx.com/Admin/autoupgrade/ajax-upgradetab.php(51) : eval()'d code on line 1