The API docs for Actions indicate that creating action conditions will default to 0 for the operator, but that value is not valid.

https://www.zabbix.com/documentation/3.2/manual/api/reference/action/object#action_operation_condition

ie. doing an "action.create" via the API and not specifying the operator results in an invalid action condition, as can be seen in the server logs:

 27429:20170207:150425.793 unsupported operator [0] for condition id [123]

And the same can be seen in the database:

Here's a comparison with an action/condition that was created via the web interface:

Looks like the default operator should be "2" and not "0" for action conditions