Prebuild cache failed

If prebuild is not working, and in Debug log you can see the error following error:

[Error] Prebuild cache (https:/yoursite.com/) failed. Error code: 500 ( Memory:55.83Mb CPU:1.02% )

that means, a PHP error occurred during the prebuild. Probably it is a timeout or memory issue, however you need to check the PHP error log to see what was it.