I was having an issue with Magento 2 cron jobs.
They seemed to be configured correctly, but every morning I got the CMS admin alert that they need to be run. The client also reported that new products didn’t appear in the frontend after saving. A sign that the database wasn’t reindexing.
/bin/sureserver-cron.sh was trying to run every 15minutes, but further investigation showed the cron script wasn’t completing.
Check the cron logs
Magento 2 cron error
[2017-09-25 09:28:10] setup-cron.ERROR: Your current PHP memory limit is 400M. Magento 2 requires it to be set to 756M or more. As a user with root privileges, edit your php.ini file to increase memory_limit. (The command php –ini tells you where it is located.) After that, restart your web server and try again.  
Raising the memory limit to 800 MB in the global php.ini solved the issue and allowed the cron script to complete.