I am using Zabbix version 3.4.13 with a postgres database back-end. After doing an upgrade from Zabbix version 3.0 it was found that hosts are not being added.  When the Discovery Action is configured to either add a host to a "Host Group" or link a host to a "Template" the hot fails to be added. When the Action is configured to only add a host and enable the host you will see systems being added to the Zabbix server. I have tested this on Zabbix version 3.0 and found this issue is not present. 

Steps to reproduce Issue:

1. Configure Action to be as follows:
   Conditions:
   Discovery check = Cyc Net 10.1.1.0 Network: Zabbix agent "system.uname"
   Received value like Linux
   Discovery status = Up
   Operations:
   Add host
   Link to templates: Template OS Linux
   Enable host
   **
2. Navigate to screen title...
3. Click on screen element...
4. ...

Result:
See screenshot...
See log file...
See memory dump...
Expected:
See screenshot....
See attached patch file...