I added "Template Virt VMware Hypervisor" and "Template Virt VMware Hypervisor" to my Zabbix Server.

Configured the correspondent macros for user, password and URL.

Started monitoring. Everything running smoothly.

However, those username and password that I used, were the personal credentials of an employee, and I couldn't keep them in the Zabbix configuration, therefore, I switched to a generic user, exclusive for Zabbix to communicate with the vSphere service.

Those new "application" credentials weren't authenticating because of a mistake on the vSphere sysadmin's side. But that wasn't the problem.

The problem was that Zabbix Proxy did keep monitoring with the old personal credentials!

I could see that because I increased the debug level for the zabbix proxy log.

I tried the following (in the following order) in order to prevent Zabbix Proxy from using those credentials, without success:

1 - Deleting discovered hypervisors (no guests template, only hypervisors).
2 - Deleting "vcenter" (main) host.
3 - Reloading configuration in Zabbix Server.
4 - Reloading configuration in Zabbix Proxy.
5 - Restarting Zabbix Server.
6 - Restarting Zabbix Proxy.

Nothing helped, except completely deleting the proxy database (SQLite3). And starting over again.

I hope that this bug was reported already, since it's very weird.