Why does Magento 2.1.2 cron:run gives Undefined index: jobs?

In my case it was caused by some cron jobs migrated from Magento 1, in core_config_data. Magento 2 expects the format to be crontab/{groupname}/jobs/{code}, while the imported ones miss the group name (i.e. default). If that is your case you might want to delete the wrong entries in core_config_data, or update them to map the new cron jobs.

I have the same error. This is the error when migration from Magento 1 to Magento 2. So I fixed it by remove all rows have "path" start by "crobtab" in table "core_config_data".

Then run this: php bin/magento setup:upgrade

And error fixed. Magento 2 will generate all cronjobs again.

As rcason said: this issue is due to migration from Magento 1 to Magento 2. After removing from "core _config_data" all the values that starts with crontab/default... (under Config Path) the problem is solved, and M2 cron jobs now run with no issue.