Steps to reproduce:

1. Create a Template
2. Create HTTP agent item to request data from an API
3. Press the "TEST" button in the item creation menu
4. Choose the option proxy and choose a proxy 
5. Press TEST

Result:
80% of the time the test fails with the following error:

Cannot read the response, check connection with the Zabbix server "{ZBXSERVER}". 

Expected:
Return the data from the HTTP URL

Extra info:
**

• Connection to the HTTP URL from the proxy is allowed by the firewall
• All necessary ports from the proxy to the server are active

This issue is only occurring while preforming an item test, when checking the data from latest data on a host where the template with the HTTP agent item is activated, everything working as expect.